if you are just hobbying, then I would choose the most feature-laden PICs in each pin size, within reason. The 16F88 is a pretty decent chip (I've used it), but the 18F1320 is very similar and the code compiles more compactly. The 16F688 is pretty cheap considering its specs, with a few pins less. For 40 pins, although you could use a 16F887, but the 18F45k20 has more memory for a couple pennies more.

What I've found works for me is to prototype with a 40-pin, then convert it to a smaller device. Some of the new 18F k-parts are cheaper than the 16F parts, and since the code compiles smaller it's almost like getting a second discount. Here are some devices that I'd recommend in pin various sizes. Most folks are intimidated by the 18F parts because the datasheets are longer, but once you can understand the basics behind reading a datasheet--and especially if you can learn one series--it gets a lot easier. It is the "series" thing that I like to stick to, when possible, to reduce learning curve. Here's my list, with two basic series for the larger devices. Note, too, that the newer chips tend to be more powerful and less expensive than the older ones. The m'chip site has a good search tool, but the one on melabs.com has a few things that mchips doesn't--such as a/d resolution.

8 pins; 12F683 (the most for its size)
13 pins; 16F688 (cheap)
18 pins; 16F883 (cheap)
18 pins; 18F1320 (powerful and cheap)
28 pins; 16F886 (cheap)
28 pins; 18F25K20 (powerful and cheap)
40 pins; 16F887 (cheap)
40 pins; 18F45k20 (powerful and cheap)