Double Sword in FFTA - Unlike it's FFT incarnation, Double Sword in FFTA only affects normal attacks, no abilities. So Reflex/Strikeback makes it totally useless, and Reflex is a fairly popular enemy ability. Concentrate is far more useful, since it affects all of your abilities, including status effect abilities.
Geitz in Fire Emblem - General Wallace is far better than Geitz. He can be promoted at 20 (if you play Hard mode), gaining more stats, and you already have two better Warriors: Dorcas and Bartre. Lots of people suggest getting Geitz, but I find Wallace almost always is better. Movement's a little poor, but since he can take on whole armies on his own, I don't really care.