I'm not claiming to be an expert in nail application and care, but people do often ask me what I use. This is what I've found works for me (keep in mind that I haven't done extensive head-to-head tests or anything, my picks are just from trial-and-error plus experience).

Everyone who polishes their nails should use top coat.  It extends the life of your manicure, speeds drying time, protects colors from fading, etc.  There are two types of functional top coat: fast-dry and normal.  Fast-dry tend to have a thicker  formula and require special application instructions.  However, once you know how to handle them, they are just as easy to apply as any other top coat.  There are also top coats for finish, ie. satin and matte finish top coats.
Unless you are crazy, I would suggest you use a fast-dry top coat for your nails.  Most fast-dry top coats have a more viscous formula, which is why some people steer clear of them, but it only takes a couple manicures before you become accustomed to the difference.  Here are the instructions that come with Seche Vite, my favorite fast-dry top coat: "Apply thickly, get a nice bead on the end of the brush, then set softly down on the first nail painted and watch how Seche Vite flows over the wet nail polish self levels and will not drag or streak the underlying manicure."  So basically, instead of wiping the brush to remove any excess, make sure you have a bead of top coat at the tip of the brush about to fall off and then apply it to your wet manicure.  Yes, wet: if you apply fast-dry top coat to a dry manicure, you will get shrinkage and your manicure will be more likely to peel off.  Obviously, don't apply top coat right after you've polished your nail - I paint each finger and then go back and brush on Seche Vite in the same order, which is the perfect amount of in-between time.  

Fast-dry top coats are also great at minimizing bubbling of your polish; I have no idea why, but I rarely get bubbling now compared to when I didn't use fast-dry.  There are quite a few fast-dry top coats and The Edge of Sanity blog did a quite fascinating blind-study on some of them, which you can see here.  The one's I hear mentioned frequently on the NB are Nubar Diamont, Poshe, and INM Out the Door.  Of these, I've tried Poshe which I found dried slower and less glossy.  Before I got really into polish, I used Sally Hansen Mega Shine Extended Wear Top Coat, which has a similar formula.  One reason I don't use SH anymore is because the bottle is opaque, so you can't see how much you have remaining; this also makes it hard to thin - which we'll get to in a minute.  Again, I think body chemistry often plays a role in which treatments work best for people, so don't be afraid to test a few out before you settle.

Another important thing to keep in mind with fast-dry top coats is that when you get about halfway through the bottle, the formula will get unworkably thick.  Don't throw your bottle out!  Just take a few drops of nail polish thinner (I use Seche Restore), shake, and your top coat will be like brand new!  You can use any nail polish thinner to thin your top coats, but many people like to match their B3F formulas, so keep that in mind.  Thinner can be used on all your polishes, not just nail treatments.  Keep in mind that nail polish remover is not the same as nail polish thinner - using remover as a thinner will degrade and destroy your polish.  If you use thinner conscientiously (not remover!), your polish can live with you your whole life!

Finally, we can move on to finish-specific top coats.  These are usually called matte top coats, although mattifying power can vary from a "satin" finish to a "flat" finish.  My favorite is Nubar V for Men Matte Finish Nail Protector, but Essie Matte About You is comparable and more easily accessible.  I find that Nubar's gives a little more wiggle room (more friendly to user-error) in dry time than Essie's.  Both of these matte top coats provide a more flat finish.  Matte top coats don't really provide protection from wear; they are all about the finish.  I will usually do a regular glossy mani and then after a couple of days, add a layer of matte top coat, since my mani is wearing down by then anyway.  All Lacquered Up has a good comparison of some popular brands and their finishes.  Here is what I have found, though not all of these are readily available:

• Flattest: Rescue Beauty Lounge Matte Top Coat or Essie Matte About You or China Glaze Matte Magic
• Slightly less flat (ie, perfect IMO): Nubar V for Men Matte Finish Nail Protector
• Suede (between flat and satin, like the Orly Matte Couture collection): NailTek Foundation II Ridge-Filling Base Coat or Butter London Nail Foundation Flawless Basecoat (used as top coat) or Chanel Suede Laquer, Maybelline Matte Maker, Barielle Matt-inee, CND Super Matte Top Coat
• Satin: Orly Matte Top, BB Couture Matte Finish Top Coat, Orly Nails for Males, China Glaze Man Matte Finish Nail Treatment