I'm stuck trying to decide which one is better: I like the flame alchemist, but the only draw back to his power is rain... he's completely useless in a fight while it's raining. The freezing alchemist isaac mcdougal is really neat state alchemist (even though he's only showed in the first episode and is killed by bradley), how he freezes his own blood into a sturdy spear and also use his freezing powers on the other soldiers so coolwhee
I personally love Kimblee (even though he is a villain), the crimson alchemist, I mean he can cause explosions just by using his powers.
Much as I want to say Ed (he's got amazing adaptability, learned earlier than almost anybody except Al, instinctively grasps complex theories quickly and so on), I have to give props to Scar. Not only did he perform alkahestry with no training, he grasped the fundamentals of creative alchemy and pulled out the Reverse Transmutation Circle that cancelled out Father's nullifier, allowing Ed and the other Amestrian alchemists to access more power than they had ever known before.
My gut instinct is to say Roy mustang, the flame alchemist; but because, as was mentioned earlier, he's useless when it rains i'd probably say Edward Elric (i knooow this is a cop-out, but he's honestly awesome!). Eds the only alchemist thats able to transform his own life source into a philosopher stone, which ended up saving his life. He seems relatively diverse in his alchemic abilities, being able to use a multitude of mediums (im not sure what he specializes in, but the majority of the time he just uses alchemy to block things or to tranform metals and concretes into weapons, so maybe i need to reavaluate my earlier statement...?). I think Roy mustang is the best alchemist, because the alchemy he fights with is tangible (the flames) where as edward uses his alchemy to create/destroy/block during a battle....Does that make sense?