If you realy want to get fully into being a PSP dev, you need every version PSP, but thats a bit OTT.
Alot of the new apps are being developed for 2.5+, because now they have wifi working, but ISO loaders only work on 1.5 and 1.0.
So its upto you, personaly i'd take a 1.5 any day. Stuff that works on 1.5 can normaly be made to work on 2.6 (plus its easier). And we can now load lots of 2.6 games on 1.5 with the various loaders. Take a trip to the maxconsole forums for more technical PSP threads.
And good luck, im going to get my self into some more PSP dev work when i get some free time.
