Boromir because they really should have let him have the ring. He would have defeated Saron, united Gondor and restored it to its original splendor, and then married Eowyn and had the cutest little kids ever.
Oh goodness, my Maedhros towel-quote made it into this thread. There really was a reason behind that particular image of poor Maitimo, I wasn't simply being gratuitously fangirlly... The other day, I was going to send him to tell the person who was playing loud music in my dorm while I was asleep to turn the music down, but unfortunately Maedhros was in the shower at the time. Thankfully, soap-suds in the hair don't dampen his effect (bad pun intended).
Er, um... Moving on....
I vote for Maedhros because my favorite character from a completely different story just lost his arm and I believe amputees should band together.