I'm sure you know that none of the flash carts designed exclusively for the DS lite will fit in you GBA- they're too small.
So if you want a cart for both systems, expect a compromise. That is you'll get it "sticking out" on the DS lite (which some people are consumed with irradicating!), so that it will be flushed with the GBA.
But with all this talk I have to ask - why do you need one that works on both systems?
The DS and most flash carts, support both DS and GBA roms so my advice would be to get a DS lite cart, whack all your sweet GBA roms and DS rom on it, and find a friend on Ebay to take your GBA away (for a fair price of course!)
If you do go for a cart for both systems I wouldn't suggest the Supercard SD - It apparently has shit homebrew support!
Regarding the comparision between supercard and ezflash, it's one of the debates that is everywhere. whether it be M3, G6, EZflash 4 etc. it's difficult to tell people what is the best as it depends on your needs.
I assume you would want GBA and NDS support, and as you say, homebrew support. Naturally, both carts support all three devices - but some better than others.
I've had all the EZflash generations and stopped when the EZflash 4 lite came out. I opted for an Supercard lite for my DS lite. Now this is just for me, but the support from the EZ flash team I found lacking and answers to important questions, and indeed and support, had to come from fellow members in a forum (as long as they weren't in the same boat!) Also new DS games needed to be patched or simply didn't work which is all I wanted my cart for.
This really put me off buying a new cart from EZflash, even though my long heritage with the company.
Like yourself I thought about supercard, the supercard team boast an almost 100% compatability for DS roms have decent GBA compatability. So supercard lite found it's way into my humble DS lite and I think it really is good. NDS compatability is spot on, and if a game doesn't work, someone on the forum has a simple solution.
BE WARNED!!! However, I haven't played with the EZflash 4 so don't think this is a direct comparision. I simply had a bunch of ez flash stuff before and now with their ND roms, I'm not impressed.
I'm sure other's will disagree, but as I said, it's hard to find a cart thats perfect for everyone at the mo.
Anyway, I hope this gives you a little idea of what to focus your decision on - it's all about support from the cart company!!!!!
If this wasn't helpful, and has just been mindless dribble (As my posts usually are!
) Try checking out the reviews on these sites:
http://gbatemp.net/index.php?showtopic=32250 - EZflash 4
http://gbatemp.net/index.php?showtopic=35982 - Supercard lite
http://www.iso420.com/nds/scmsd/index.htm - Supercard SD (for both GBA and DS)
PS - If you do get a supercard lite DON'T get the rumble, they don't support GBA - Few forgot to mention that!
Anyway peace out brother, happy flashing!!
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