Omgawd, I cannot decide between Shield and Staff at the start! D: More MP and learning MP Haste earlier on would be amazing. But learning Second Chance (Shield) early on would also be quite nice... Hmm.
Sword: Glass cannon route. You quickly gain access to some of the strongest offensive abilities, start with a higher attack stat. You also get all of the support abilities at a reasonable level range (Scan, Guard, Second Chance, etc) but your defense is shit. Oh and you don't get Leaf Bracer haha...
Staff: Balanced / Magic route. You gain access to all of the magic based support skills early on, and all of the strongest magic based combo enders in the game at compartively early level. You also gain access to one extra MP, though the downside is that you basically lose out on certain useful skills (Second Chance, Counterattack and Combo/Critical Plus skills) since they're obtained at a late level.
Shield: Defensive route. You quickly gain access to all of the defensive/suport skills (Second Chance, Tech Plus, Stun Impact, Leaf Bracer etc) and start with a higher defense stat but you completely miss out on offensive skills for the majority of the game.
So to sum it up
-Sword turns you into killing machine, and if you're good at avoiding hits its a good path
-Staff gives you a ton of option (You're good at Magic AND Strength), and it's probably the most consistent path
-Shield makes you harder to kill and is probably the "easiest" path (but not as fun as the others imo)