What are you painting ? If it is a piece of furniture for example, you could definitely follow carrust's excellent advice.... if it's a boat, then you would need specialist paint...if a painting, then oils are good.... it really depends on what it is and what sort of knocks and treatment it is going to receive as well !
I had a very old set of bedroom furniture which I loved the look of but hated the finish, so I sanded it down, painted it with an undercoat, then a top coat in water based gloss (actually two coats), then hardened it off with a polyurethane matt varnish to protect against my dyson....
Woodwork (already painted) seems to just need a good sanding down, then a couple of coats of gloss paint - but apply these really thinly and it's a good idea to give the first coat a quick rub down with some fine sandpaper to get a really good key. Unpainted woodwork deserves a primer or undercoat before the final coats (once again, sanding lightly between coats).