Since I'll want the option to be able to play my game backups from whichever system I choose, I'll need a decent-sized memory card (16GB+) as games are often quite large (1GB+ each).
The PSP Go uses M2 memory cards. 8GB is £16 and 16GB is £50.
The 1000-3000 use Pro Duo. 8GB is £15, 16GB is £25 and 32GB is £50.
I have used Play.com for those prices - I doubt other retailer's prices will stray too far away.
I think I'll have to stick with the 1000-3000 series due to the memory card prices.
More specifically, a 3000 (due to the better screen than the 1000/2000).
The 3000 is £70 on Amazon.
I'm researching second-hand prices of the 3000 as we speak
CEX are doing a second-hand 3000 for £65. Rip-off.