where are you going on vacation? if you're going anywhere with plenty of sun, I'd bring at least a couple different sunscreens. I just came back from hawaii, and a few hours on the beach sans sunscreen = sunburn, as my sister learned lol.
-especially if you'll be out all day and don't want to be weighed down by a heavy purse, I'd get a travel-sized sunscreen--you need to re-apply sun protection every few hours.
-I use a strong UVA/UVB sunscreen for my face, mainly because it tans kind-of blotchy otherwise.
-a spray sunscreen is easiest for places like the beach (kind of gross to re-apply a liquid sunscreen on skin covered in sand and water). keep one handy in your beach/pool bag.
-I just use regular sunscreen on the rest of my body. I'm kind of lazy about applying sunscreen to my legs, but I'd definitely wear some on your decolletage (neck, shoulders, etc) since that's where I usually get burned.
all the sunscreens I use are from neutrogena, and I don't really have any complaints--they're not greasy, they don't contain parabens, etc. my mom swears by the la roche posay athelios sunscreen though, if you don't want to use drugstore products.
either way, I agree with the previous post that you should use high SPF--although FDA regulations are pretty lax--a ton of sunscreens aren't full-spectrum, and something claiming to be SPF50 might only be SPF30.