353 is the harder level, but if you can get to the very bottom where the playing area goes full width, you can rack up huge scores on your final move when special gems explode and then make more, repeat, repeat.
There's quite a few levels where it's imoossible, as far as I've seen, to get three stars. I wish storm8 would fix them. I'm trying to get three stars in every level. I've got to about 450 so far, three stars in every level except about 10 levels which are really difficult. I'll have to come back to those, I think.....