It depends on what you're trying to do, and what kind of resources you have. Polyurethane is the best finish for guitar necks/bodies, bar none. It's impervious to just about anything short of methylene chloride, Rottweilers or hateful spouses, it's super-durable, it's able to be brought to a fine gloss, etc. Problem with it is, it can be difficult to deal with if you want to spray it due to toxicity issues. There are brush/wipe on versions of it, but they generally don't produce the kinds of fine finish you expect on a guitar. It's difficult to work with once it's cured, so a less-than-perfect application can make you cry. It's difficult to repair, so you've gotta be a talented applicator and willing to tolerate signs of abuse later on as they occur.
On the other hand, lacquer will produce as fine a finish, but it's a lot more work to get there and not quite as durable. On the plus side, you can work it forever. Makes it a favorite for us DIY folks, all talk about "tone" notwithstanding. You screw up, you can fix it, and you don't need a pro paint shop to deal with the whole thing. Allows you to try all sorts of schemes, such as burying decals.
Everything else is just also-rans that aren't worthy of consideration on a fine instrument.