I use (at the moment) a Wacom Intuos, The entire tablet is about the size of a sheet of A4, perhaps a small amount larger. Previous to this I have used earlier versions of Wacoms - one an A4ish and one around A5 size. I had both of those at the same time and could swap between them. Prior to that I had a cheaper brand, a bit larger than A5 and I forgot, an A5 ish one in my work place, cant remember the brand. All of them lasted years, so choose carefully.
Points worth finding out about or worth knowing:
1. How big is the working pad area compared to the entire pad area - they have quite big margins around. My pad also has 'buttons' at the side you can customise which increases the pad size as they take up space.
2. Do you want customisable buttons. I was annoyed to have them when I bought it then found they were very helpful if you sit with it on your lap away from the keyboard. They can trigger features and zoom the screen in/out as well as other stuff.
3. Pads can have customisable work space - you set the parameters of how much work pad you wish to use, so you can make the pad size effectively smaller by setting different boundaries if you want to reduce hand movement. I do not know if all pads now do this.
4. Will you work with the pad flat on the desk or on your lap etc? The much larger pads need desk space and dont fit on laps. Middle and small are OK, I often do not use the desk surface.
5. If you are travelling lots, get a smaller one. Get a pen shape you think you can hold for long periods comfortably.
6. Using a small one is not much different for basic stuff, maybe a really keen artist would find more difference. The actual working area on my pad is quite small, Maybe 7x 4 inches. I dont have a ruler to hand. The whole pad though is as I said a bit bigger than A4. There is no issue at all for me with a working area this small, I am very happy with it. Detail work and moving about the screen is not an issue.
7. Different brands offer additional different pen modifiers and spares, some offer no alternatives.
8. Dont get a pen that has a battery in it, its a pain.
9. Some of the tablets can be run by wire or by an adaptor that makes them wireless. This is an added cost. I have not bothered with an adaptor as I like my stuff to keep working without battery issues and wires don't bother me at all. If you use a wire,make sure it is replaceable, Wacoms seem to be now, they just plug in a standard cable. My last tablet failed due to the tablet to pc wire fatiguing, it was moulded on to the tablet so could not be replaced so the whole thing had to be scrapped.
10. I think tablet sensitivity is in lines per inch. Reputable tablets will openly state their sensitivity - the higher the number the more sensitive. If they dont want to tell you, they are hiding that info for a reason! Some also are sensitive to pen tilt, which is of use to artists.
11. Tablets are great fun and I never use a mouse now, not for anything at all - it seems primitive compared to a tablet. Also less repetitive strain risk from a tablet.
12. make sure you can get extra replacement nips for the pens in addition to the one in the box
14. When you get your pen, show it to all your housemates and tell them it is not a biro, but very expensive, so when it willl not write, they are not to just throw it away!
15. You can change the speed of travel of you pen across the pad in the software (check before you buy) so again, this allows for working on different size tablets easily.
16. If you can find a graphic designer forum or a retouching forum it might be worth asking your questions there as well. Try RetouchPro forum - free, helpful.
17. I know 2 or 3 people who moved to tablets. They all hated them for the first 2 weeks and then they loved them. Persevere if you find a tablet/pad difficult initially, you will be so glad before very long.
