Which is the better one to go for and why?

Get the DS version since that way Team17 AND Two Tribes make some money :)

They are both great, I suggest just getting the version for the system you use the most and if your friends like worms then get the version for the system that they own.

PSP because you got hats

Definately the DS version. I bought both since I have both handhelds. But even though they are both cool and all, I don't really consider the PSP version "handheld". I mean, it takes ages to load up an online game and play. Whereas it takes less than a minute on the DS :)

I bought a silver PSP and WOW2 tuesday and I really fall in love with the game & the consol.
This new Worms is really like a WA version II !
For me, it became just the best Worms I never played before.
Unfortunetly, I didn't test the DS's version and I can't give you any opinion.

PSP because you got hats

In DS you got exclusive minigames
2 screens
Easier Landscape editor (IMO)
Touch screen controls
Easier Online mode

DS because of the touchscreen/microphone functions (e.g. for the minigames)

i like the DS version better

Looks like most people think the DS version is the best so far

I put about equal, since it seems as though they both have strengths and weaknesses. I haven't played the PSP version, but based on what I've seen and heard so far, it seems as though the DS version is better in terms of gameplay and the size of its user base (important in an online game), while the PSP version is better in terms of graphics and customization.