The main thrust of this site is to give as much information as possible about the pros and cons of various telescopes. But having thought about it and after reading the many queries that newbies post on forums such as the Stargazers Lounge, I have decided to try a different approach based on age and health. Most of these comments will have been made elsewhere, but putting them in a different way may be more helpful to some. So here goes...
For youngsters up to the age of about 11 or 12. Which will probably mean that the parents are buying, possibly because the child has expressed an interest or because the adult think he or she might be interested.
In this situation a decent, reasonably light pair of Binoculars would be a good starting point. Even if you are certain the child really is interested and will eventually want a Telescope the binoculars will still be useful. Perhaps the most important point to note is the weight of the binoculars. If they are too heavy the child won't be able to hold them steady enough to see anything worthwhile.
If the decision is to go for a telescope then the size of the child is the next consideration. For a small child the table top Skywatcher Heritage 76 Dobsonian will be easy to operate and give good views of the Moon, the belts of Jupiter and it's Moons as well as some of the brighter deep sky objects like the Orion Nebula and the Andromeda Galaxy. And it is cheap - perhaps as little as £50. But the rings of Saturn will at best be little more than small ticks sticking out the side. So with a bigger child the larger Skywatcher Heritage 100p at around £90 would be better as it captures twice as much light, whilst the Skywatcher 130P Dobsonian at less than £140 could prove even better. Just as easy to operate and able to give you much better views - the mirror captures nearly 3 times as much light as the 76mm one. And probably a good choice if you want to share your childs interest.
For teenagers. This gets a little trickier. Again the chances are that the parents will be buying, but the expectations and knowledge may be much greater. But Binoculars may still be the first step, possibly with a decent tripod. If that isn't acceptable then, depending on finances, a small portable Refractor or Reflector up to about 4ins aperture, or the Heritage Skywatcher 130P Dobsonian mentioned above. The Skywatcher 150 (6") Dobsonian will do even better for around £200.
If light pollution and/or impatience is a problem then a GOTO scope will be well worth the extra. The Skywatcher 1145P Synscan AZ GOTO costs around £250. It will give good views of the Moon and Jupiter and is capable of capturing many of the brighter deep sky objects under dark skies. Larger aperture GOTO's will enable you to see even more but the cost increases considerably. And do buy from a reputable firm rather than a high street store or toy shop, unless you have taken advice about the scope you are interested from a knowledgable person - perhaps someone you have spoken to at a Star Party or the local Astronomical Society.
And First Light Optics have a Beginners guiden which is well worth looking at.
You have retired or the children have left home and you now have time to spend Stargazing. Although money is the first thing to consider, the other is your state of health. If you suffer from any form of disability, have any sort of back problems, suffer from chillblains or simply don't like the cold then these considerations should be at the forefront in your choice. A constant comment that you will see on the forums is 'I didn't realise how big/heavy the Telescope would be'. Not much fun if you have to carry it any distance. And if you really don't like the cold then, unless you are prepared to spend a lot of money buying yourself an observatory, you aren't likely to use the scope much at all.
So given these potential problems the viewing position is a very important consideration, especially with the initial alignment. Anything much higher than 30 degrees in the sky will present problems if you have to do this alignment using a straight through finderscope or a zero magnification red dot finder. And if you also suffer from light pollution the chances are that you won't be able to see anything through the red dot finder other than the very brightest stars anyway.
Newtonian Reflectors and Dobsonians also suffer from the fact that you can end up with the eyepiece in an 'impossible' position which requires you to rotate the tube in the supporting rings. Not easy to do with cold fingers and, if ice has formed on the tube, which happened to me once, a disaster waiting to happen. There are devices to help you overcome this but they don't come with the scopes!
This is where the SCT's, the Schmidt-Cassegrain and Matsukov (MCT) type of Telescopes are so much better suited to the old and infirm, both by reason of their relatively small size, portability and the fact that the eyepiece can always easily be rotated to a convenient position. The downside is that, inch for inch of aperture they are more expensive. And they are generally reckoned to be less suitable for AstroPhotography because of their longer focal lengths and even more so if they are on the Alt-Az type of mount. Having said that I have obtained quite good results with an f/10 SCT on an Alt-Az mount so these facts shouldn't be something to worry about unless you are dead set on AstroPhotography.
So what scopes to buy? Well, if you don't want to spend too much or are not certain that astronomy is for you then perhaps you might even want to start off with the table top Skywatcher Heritage 76 Dobsonian mentioned above. Not an SCT and won't get you very far but a start. However, if you are more serious then the Skywatcher Skymax 127 SupaTrack Auto (5" Maksutov) at around £320 could be a good starting point as it is reasonably light and portable and is able to gives good views of the Moon, planets and many of the brighter deep sky objects. But although it will track objects it won't find them for you - it isn't a GOTO scope.
If you want a GOTO SCT or MCT with a decent aperture then you have to pay considerably more. The 5in Celestron NexStar costs around £680, the 6in one costs around £740 and the largest 8in costs around £1,130. These will all require the use of a portable power tank at around £70. And of course if you get hooked there are all the extras which I have mentioned on the other pages. All the images currently shown on this web site have been produced using the Celestron NexStar 6SE, at first on the Alt-Az mount and latterly using a wedge. But remember that apart from the stars themselves you won't see any colour when you look through the scope at something like the Ring Nebula as shown here. It will only be a faint smudge - see Beyond Reality for further comments on this.
The Celestron NexStar Evolution is an even newer updated NexStar SE range of telescopes which it is claimed can be controlled wirelessly from an IOS or Android device with the free Celestron app. They have their own built-in lithium-ion battery which will last up to 10 hours so that you don't need an external power source. These must eventually replace the current SE range. The Sky at Night September 2014 magazine has a very favourable review of the 8in version of this scope and it is the only time I have seen them give a 5* rating overall.
You are a busy working adult, perhaps with a family or other commitments. For you time will be the limiting factor as the likelihood of clear skies coinciding with a free evening may be small. For you the 'Grab and Go' kind of telescopes may well be the best solution. Relatively light and portable and easy to set up quickly. But if you are reasonably fit you don't necessarily have to limit yourself to the smaller apertures though anything beyond 8ins won't be that portable. Probably the limiting factor will be your budget and for ease of use, cost and aperture the 6 or 8 in Skywatcher Skyliner Dobsonians are hard to beat. But they aren't GOTO scopes and if you feel you need one of these then two to consider are the Skywatcher Skyhawk 1145P Synscan at around £250 and the larger 127 version at about £360. For larger apertures the costs go up considerably as does the size of the scopes.
Please note that all prices quoted are approximate, subject to change
and for guidance only