I almost take them together and then team them up with Celes and Cyan in the WoR. In the WoB it is better to choose Edgar, cause hos Autocrossbow can do actually a lot of damage to many enemies. In the WoR you go with Sabin, cause in the beginning of the WoR you also take him at he levels up very fast then. Also both are very strong because you can have them that early in the game. You can very easily boost their magic because 9 of 10 times, you will have one of them in your team. Edgar was for me the first charachter that learned all the spells, Sabin was second.

If you want attacks who can hit every enemy and all so simple attacks that do heavy damage to one enemy choose Edgar.
If you want a little challenge and try to press the buttons right for the Blitz's then choose Sabin.
Or if you want a combination of those two choose them both.