What's your favorite power tool?

I bought a Ryobi 18v inflator/deflator a few months back, and it's the best tool I own. I don't have a compressor, but this thing lets me keep all the tires in my fleet inflated, which is necessary more often than I would have expected. The set pressure function means I can leave it alone while it pumps up the massive tires on the stock car. Since it's battery powered I can take it to autocross, a friend's house, or even just out into the driveway without unwinding 40' of hose. It's awesome.

Runner up: my 1/2" drive impact wrench

Tough call.  I think I'd have to choose my electric finger sander from the Hammer Store when combined with the 3M Cubitron or whatever sanding belts.  It accomplishes things that are nearly impossible with any other tool I own.

Runner up would be my 3/8 electric ratchet.

1/4" impact driver, I use it for just about everything, including cleaning the shower.

Toss up between the Milwaukee M12 stubby impact and the M12 drill. 

Wait, is a lathe considered a power tool? If so, that. 

Does the plasma cutter count? It uses power and it's my hands down favorite tool.

iATN.

Snap-On Super Duty long barrel air hammer.

I've never had a suspension component not come loose using one of these. Chisels out frame rivets great too. No more drilling B.S., chisel the head off, then punch the rivet out.

Dremel 4300.

If you do any kind of hobbies, you'll wonder how you survived without one.

If anyone says needle scaler, they need to see a psychiatrist 

M12 Ratchet - saves so much time when wrenching on things.

Millermatic wirefeed... 

60V Dewalt angle grinder.

It has replaced my corded grinder for 95% of the jobs I would use them for.

I'm gonna say my 1/2" impact, simply because I went for so long without a compressor big enough to run it, and I remember what chore it always was taking a set of wheels off with a breaker bar.

Snap-on cordless electric 1/2" impact. It makes junkyard teardowns soooooo much easier. Cordless Sawz-All is pretty great too.

Toss up between my DeWalt impact (I swap tires a lot), and one of these: