what to take? its for ds lite
Well, you've recieved a lot of opinions about different carts, and I'll throw mine in as an EZ V owner.
The EZ V runs very stably- very few games have issues running at this point, and I personally have never had to wait for a "compatibility update" to run a game on the EZV. You do, however, have to find out the save type (the EZ V does not have automatic detect, it relies on a save type database). However, between the old maintainer cory1492 and the new one (Mosqto), it's very rare to wait for more than a day (usually it's hours). The EZ V has a physical savechip; the downside is that it takes a few seconds to backup the old save to the MicroSD and load the new one to the savechip; the positive side is that 99% of games work without a hitch. The built-in support for the 3-in-1 is great too (rumble, Opera, and GBA games), and we have a smaller but dedicated community.
I've heard a lot of great things about the R4 personally, and it has an extremely large community. It's still developed for extremely frequently. I can't speak for the cart personally. It is possible to use the 3in1 with the R4; you have to get a prepatched copy of the Opera Browser, get a tool to put games on the 3in1, and I'm not sure how you get the rumble to work.
The CycloDS is another cart I've heard great things about, but it's still pretty early in it's lifespan, and I've heard a lot of issues about stability. The new feature developments and MicroSDHC support are definite pluses. From what I understand, it has built-in support for the 3in1 (rumble & Opera), I believe you still need a seperate loader for GBA roms, but it isn't hard at all.
Overall, I'm really happy with my EZ V, and it works stably, the build quality is good. If I were to buy a flash cart today, it'd be between the EZ V (stability) and CycloDS (new features + SDHC).
EDIT: I followed this link from the main page, so I didn't see it was in the R4 forum. The R4 may be a great cart, but this isn't the most neutral place to put it