I would install the faucet last. You don't want to worry about dinging up the faucet by getting your splashes in place. Also, it will be a lot easier to put your caulk down cleanly w/o having to work around the faucet.

Depending on what kind of top you are using, you might want to attach the faucet to the counter top first. For example if the sink is too bulky towards the bottom, it can be tricky to attach the faucet from underneath. Also, clear silicone sometime looks better than white cocking, keep that in mind when you seal the edges.

Here is a link that might be useful: Bathroom Vanities

I'd install the faucet before putting the vanity top on. Easier to tighten up the nuts if you aren't laying on your back inside a cabinets.

Agree, if feasible I install the faucets before installing the top.