I would recommend the A1200 with a cheap 2.5" drive and some sort of Fast RAM expansion (any will do). With this, you can code assembly, do music tracking, play games from WHDLoad, browse the internet, do some 3d graphics, and do word processing. I'm much the same as you; 18, new to the Amiga and interested in doing the same things. My primary system is an A1200 with 4MB Fast RAM, a PCMCIA ethernet card, and a hard drive.
An A500 would perhaps be easier to find, but it does not normally support a hard drive and is not as powerful as the A1200. Of course, it is the "classic" Amiga.
If you have the money, an A4000 is amazing. Of course, the A2000 and A3000 are good as well. The A1000 is an interesting piece of Amiga history, and when expanded to 512K/512K, it can do pretty much exactly what the A500 can.
Of course, this isn't even considering the vast amount of alternative Amiga setups/systems (MorphOS, AROS, WinUAE, MiniMig, AmigaOne, Pegasos, XAmiga, Amithlon, AmigaForever, etc).
