Eh, hard to say but I guess I would be Al. Or maybe leutenant Hawkeye. Heh, Havoc is kewl too ^_^ he reminds me a lot of the Australian scientist in D. Gray-Man.
Scar is one of my favorite characters, but I wouldn't want to be him (bearing the guilt over killing innocent people, getting shot at, being chased by homunculus, having a price on your head, etc.)
I would want to be Hawkeye. She's so cool.
If I could be a homuculus, I would be Lust. She's so cool, and I love the the nickname, "Ultimate Lance." I like Wrath too, since he can fight with four swords.
Haha, for me it'd be Greed, too. He's just to awesome. If I had to choose a female character it'd be... argh I don't know, maybe the Housewife Master?? So far I haven't seen a female char that has left a bigger impression on me (in comparison to the male chars of course, the women are certainly more interesting than the ones in some other mangas.)