IMO the 35 Single Step is a better boat.
 

We test drove both the 35 single (which we bought) and a new twin-step on the same lake in similar conditions one day apart.

To us, there was no question that the single-step was much more responsive in the water - it would turn circles around the twin-step, which tended to bounce a bit when you threw it into a hard turn, while the single turned like it was on rails.

As far as comfort going down the lake, I've been told that the twin-step will give you a softer ride in rough water, but we didn't notice a difference between the two in medium chop on Lake Cumberland.

As far as speed is concerned, there's no doubt that the twin-step is 3-4 mph faster with the same power. Our passengers thought that the back seat in the twin-step was to low and made it difficult to see out. All around, we agreed that the single was both a better looking boat and much more fun to drive because of its superior handling. Even if the boats had been the same price, (which they are not - the twin-step is at least 40K more) we preferred the single-step.

But that was just our experience with two boats that we drove. Your Results may vary :)