#5: Bowser: Though the heaviest of the heavy, Bowser is decently mobile, with the all-round strongest smashes in the game. He has a decent aerial game as long as you can cancel the lag, and his special moves are good also.
#4: Charizard: Surprised huh? Charizard is a really good heavyweight. Lots of fast smashes that are fast as well. His special jump has super armor so you can plow through people. He can glide, and his Rock Throw has Super Armor and can do 45%, the strongest Side Special in the game!
#3 Yoshi: Though a very small heavyweight, Yoshi can still take a good amount of damage. Hes fast, small body comes useful to him. Having the highest mid-air jump in the game, packed with super armor, it will take a GOOD blow to stop him (not including F-Hop). His B-moves are a good gimping tools, and his smashes are strong, but not nearly as strong as Melee. D-Air is still the best aerial in the game. 
#2: King Dedede: The Bowser of Dream Land, Kind Dedede comes packs with his Waddle Dee, Doos, and Gordos, and his hammer that becomes a rocket hammer. His crazy special that makes his do a funny dance is actually quite messy! 5 Jumps and his special jumps that has Super Armor during lift-off.
#1: Snake: I hate to say this one too. His tactics actually take some thinking cuz you have to pretend your being sneaky. HIs smashes are increible strong, with the strongest F-Smash (in terms of knockback) in the game. His recovery has Super Armor, and you can use his Down Special to regain his special recovery. He is hard to kill. Quick tilts and aerials also make Snake a quick Heavyweight.