Sabin actually has a wide variety of equipment at his disposal. Here's a table of all the items that can be equipped to Sabin as well as my personal preferences for when it comes to equipping him.
Kung Fu Suit
I personally don't use many weapons with Sabin. His blitzes attack pretty hard without them, so he doesn't really need them until way later in the game when he gets Tigerfang and Godhand (which you can only get in the GBA version of the game), and those are both free. If you're playing the PS or SNES versions of the game, I recommend keeping Tigerfang on Sabin as soon as you get it. It tops any other weapons he's able to get in the game.
I've heard from various players that Tigerfang should be used in the GBA version, too, but I think using the Tigerfang or Godhand is really up to each player and how he or she is using Sabin. If you use him as a mage like I do, Tigerfang is definitely your best bet because it boosts your Magic Power. If you're using him as a fighter, Godhand is going to be better, simply because it's stronger. Sabin's going to be fairly weak at this point in the game if you're only using him for physical attacks, so why not use something that gives his attacks a harder hit?
As for defense, let me tell you something you probably already know: As good as Sabin's HP and attack stats are, his defense sucks, and there's very little you can do about it. Because of this, you're definitely going to want to put Sabin in the back row (It's okay, because his blitzes attack just as hard there.), and you're definitely going to want to take use of shields, helmets, and armor that's available to him. In particular, giving Sabin a shield is probably the best thing you can do for him. Any shields and armor (pending they don't lower his stats) will be better for him than nothing, unlike most of his weapons which don't really do anything for him. There are, of course, pieces of equipment that are better than others, though. The Red Jacket is his best armor, and the Genji Helm, Circlet, or Green Beret are arguably his best helmets depending on what you need, so keep those on him once you can get them. I use a different shield every time I play the game because I feel like I need different things from a shield in each playthrough. Some boost defense while others boost attacks, and others even absorb magic. Use what you need at a given time, and don't be afraid to switch shields when something better to you comes along.