Well when you say "easy to use," that falls into these categories: Good recovery, simple and effective attacks, hard to punish, low inputs, decent weight to survive attacks, hard to combo, and trade heavy. So I think the character that falls into all of this is Peach; her jump/float alone makes her recovery good, with the added benefit of an almost un-punishable Up-B, unarguably makes her recovery insane. Plus since she is floaty she is very hard to combo allowing her to take less percent, with combination with her weight, she becomes very hard to kill. Her D- Smash is simple extremely effective, and almost impossible to punish, her dash attack is incredible, her aerials are amazing (combination with float becomes god like), and her Forward throw actually kills. Keep in mind everything I mentioned do not need much skill, and can be picked up easily. Plus she has her Turn-ups which are stupidly good.
Look even though I am a Sheik main, and my view might be "bias," I still do not agree that she falls into the category of "easy to use," since she requires very precise attacks, effective movement (with shield dropping being almost a requirement), not to mention how ridiculously punishable and easy her recovery is to edge guard. I play Falco, and I find him easier to use then her.