I for one say that either way works fine, though personally I only ever watched through the subbed versions of Fullmetal Alchemist and Brotherhood completely. Both of them seem like they fit the characters well enough and are easily sufficient.
On another note though, I personally suggest only watching Fullmetal Alchemist: Brotherhood. If you HAVE to watch the first anime, do it before Brotherhood or your opinion of it will significantly lower. Brotherhood>1st FMA in almost every way, and the jump in quality as a story is pretty huge if you go from one to the other.