I personally perfer the Super or Mega Mushroom because it does the most damage the easiest way. The Pow bloacks are easy to dodge, all you have to do is get airborne. The Rainclouds are quite easy to pass on because you never get them in first place, usually in the middle of the pack when it is easiest.

It sucks though when your on 150cc 5 car lenghts from the finish line and you get lightning, seeker shell (blue shell), red shell, Pow block