Ueki no Housoku, Katekyo Hitman Reborn! Recommendations
Just like Reborn!, it has great comedy plus action done right. If you liked Reborn due to the battles and different battle styles which always keep you guessing, you'll like The Law of Ueki. The battles in this series always keep you guessing and are never dull or the same thing over and over again like other Shounen series. Reborn! and Ueki are two of the best Shounens out there.
Very similar in various aspects.
Art is very similar.
Characters resemble each other in personality.
Both involve the main characters making friends, gaining powers, and going on some sort of a "journey" together. In both they are end up working to better humanity whether they know it or not.