Well, Wacom has come out with a new $100 stylus for iPad which is supposed to be pressure sensitive. I haven't tried one personally. A regular capacitive stylus for iPad is not pressure sensitive and both styli have large rubber tips that take some getting used to after drawing with a pen/pencil size tip with Wacom etc., digital tablets.
If you already have an iPad, get a regular capacitive stylus for around $20 or so and test it out using apps like Procreate and Brushes. Then you'll get a sense if drawing on the iPad is right for you. You won't have the precision with that as you would with the following types of tablets without a lot of zooming in and out though.
As for digital drawing tablets, there are basically 2 kinds, the sort where you draw on it horizontally on desk or lap using a special stylus while looking up at your computer screen, and then the expensive digital monitors where you use a stylus and actually draw on the screen (tilted +/- horizontally depending on preference).
Wacom is the leader but there are other brands too, usually for less $. For a long time people said that Wacom's models really didn't change much, maybe appearance updates. That no longer holds true. They recently merged the Bamboo (beginner) and Intuos (professional) lines and these are the first types of tablets. Their top of the line Cintiqs are the sorts you can draw on or use as a second monitor. They've come out with the bluetooth pressure sensitive stylus for iPads, and even their new Cintiqs are getting more mobile: smaller & wireless.
When doing your research, I'd recommend you check out Ray Frenden's digital tablet reviews:
http://frenden.com/tagged/review
He's reviewed assorted Wacoms, Bostos, Monoprice, Yiynovas, Huions, etc. Based on his reviews I bought a Huion 610 tablet on Amazon several months ago for $55 (which was half the price I paid for my previous Wacom Bamboo --and the Huion has much,
much better pen sensitivity.)
Using a tablet to draw takes a little getting used to at first, but it doesn't take long, and you'll really be glad you got one.
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Good luck!