I am using a Wacom Intuos 4 - maybe it's a "bit" overpowered for PA, but it was a present. It took me some months to get perfectly used to it, my lines are still more confident at paper but it's a great feeling to sprite with a tablet compared to a mouse.
-The biggest advantage is that you can draw with a tablet like on paper which is very good if you are used to draw or paint with any traditional media.
-Creating Pixel art with a tablet adds a much more painterly approach to it
-A tablet really helps a lot in the early stages, if you are blocking in colors it's much easier to create accurate shapes.
-A tablet saves you lots of time.
This took actually ~45 minutes with my tablet,
(It's only a sketch, more like Oekaki but you get the idea how it could look like if I'd spent another hour with it) it's impossible to work with a mouse while maintaining the incredible speed and control a tablet would give you.
-I am using my tablet for sketching&detailing pixel paintings.
-I don't use it for any kind of manual selection - as long as I am using the common tools I have a pretty good workflow with it.
-I also don't use it for detailing low-res sprites and animations (usually thare are a lot of manual selections to do and it's not worth to change between mouse and tablet)
-but I use it for shilouetting low res sprites and raw color block in.
I won't be able to sprite without a tablet any more, it's just to comfortable and it completely changed my workflow. I sprited without a tablet for about 1 year and after all I'd say that each ambitious pixel newbie should try to sprite with a tablet as soon as possible.
IMO a combination between mouse, keyboard and tablet is perfect.
Edit1: Regarding to the mouse: you definitely should get a high precisely gaming mouse, if you don't already own one - those work really good and they are definitely better to draw than cheap ones.
Edit2: A friend of mine bought a cheap Wacom Bamboo tablet and started to work with it. He said that it's good enough for him and I thrust him, so if you don't have lots of money it'd be a good idea to start with this tablet.
Spriting 24/7 isn't fun after all.