It depends on your play style and what you might consider fun. For example Paragon requires a lot of babysitting and micromanaging. Personally I beat the game using Taggins - I really liked his shield and strong attack. Kate in my opinion is also very solid. I actually ended beating world 1 with Kate and when I reached level 10 with her I switched to Taggins on world 2 - it seemed like a waste playing with a maxed out hero to me! As for the premium ones, I wouldn't bother as they seem over powered, except for Fate which I personally didn't enjoy as much. The Mark X (tank) seems more like a cheat than anything.