Well PSP 1000's will always be hackable those are the big fat ones, they are old but the homebrew capability is the highest on that. PSP 2000's are the first slims released, about 80-90% of psp 2000's are hackable some have a new motherboard chip in it which is unhackable, and psp-3000s for now are un-hackable, actually i shouldnt say that, they are working on psp 3000 hacks but it wont be completely hackable for a while.
for me, id go with a psp phat (psp-1000) although they are old and have half the ram of a slim, psp 1000's sit nicer in you hand, and theyre always hackable, you cant really lose with a phat, and the screen on a phat is not exposed, what i mean by that is, overtop of the screen is a layer of plastic, so if you tend to drop electronics it could help
oh and psp 1000's you cant really buy new, but u can get one at a pawn shop for pretty cheap, or u can get one off ebay
thats my 2 cents, hope it helps