3in1 + R4, you can get an R4 fairly cheap with a 1G card, and while you are at it throw on a 3in1 for $15-20 extra. There is a decent program out right now to make use of the 3in1 from any slot 1 cart, and I have been putting in tonnes of work making a menu these last couple weeks for making the most out of the 3in1 (not to mention, with a patch file I made a while back you can also use opera with 3in1, and 3in1 can act as memory expansion for dslinux now too).
It's a decent combo, the simplicity of R4 and GBA support with 3in1 (just don't expect a G6 out of the 3in1, it only has 32Mbytes of flash).
BTW: love my EZ5 too, enough that I keep updating an unofficial save list. It does a few things that R4 cannot for me, chiefly it gives access to the SD card when booting homebrew with wmb, it allows me to replace the menu program with anything I like, it is much more solidly built hardware wise, and more... but for strictly games R4 is great (once you are aware you may need to dismantle it to get the sd slot working again when (not if) the spring breaks).