I use a Woody kreek'r 196 40 degree offset. I have paddled with almost every different type of offset, including 90, 75, 60, 45, 40, 30, 28, 12, and 0. I personally prefer the 40 degree offset because it is still a flat enough offset to make freestyle moves easy (ie loops, which are easiest with a 0 degree) and I like the power I get out of 45 degrees for a forward stroke. I prefer the stroke power over freestyle ability.
The offset will not make your roll any more powerful, imho. However, the length of the paddle will. Longer paddles give you more power in your forward stroke, and in a roll because you have more leverage off of the blade. Shorter paddles are good for freestyle because the blades don't get in the way as much, but they have less stroke power (because you don't need power, only a large blade to plant your moves off of). (FYI some creek racers use paddles up to lengths of 202 to get more power out of every stroke)
The grip width also makes a difference. A wide grip is generally prefered for freestyle because you are mostly throwing off of a planted blade and don't need much forward power from the paddle, because your body is moving around itself, not in a direction. (ie your center of gravity does/should not change when you are cartwheeling etc.).
A narrower paddle grip (not less than a 90 degree bend at your elbows!) will give you more power in your strokes and therefore your roll because you are increasing your leverage by having more paddle shaft on the outside of you hands.
All of that said, it is best to work on your roll without a paddle. Hand roll, hand roll, hand roll! I don't agree with purchasing a paddle to "strengthen a roll" because a hip snap and good roll technique should make your roll strong enough so that you don't even need a paddle.
I'm sure others on this forum will disagree with the above, so please feel free to give your view.
Oh, I love the paddle because it feels so strong, and the blades float nicely to offset the wooden weight. The paddles are amazing. If you want I can loan you a demo to try.