18 TSW Mondello which offset?
 

I'm looking at either the 18x9 with 20mm offset or 35mm offset. The lip of the 18x9 is bigger than the lip for the 18x8 (comes with 40mm offset) which is why I want to get the 18x9's. I don't really understand the effect of different offsets.

Also, for those of you that have 19's have you found any performance advantages/disadvantages compared to the 18's I kinda want the 19's but the jump in wheel and tire price sucks.

Any help would be great, thanks.