with lipo the power delivery is the same right through the run 20c lipo about the same as nimh but 30c and above are just awsome i mainly race on road and there is no comparision if you can get a 30c lipo then buy it
nimh are better or easier when it comes to weight at least you dont have weight the car down with 2 house bricks to get it through scrutineering
but at the end of the day a lipo is faster if you can keep it on the island for 5mins
hope that helps Andy