I am currently running 225/50/16 tires and I'm planning on getting some winter tires.

Should I stick with the current size or go a tad bit narrower and get 205/55/16?

I actually think I get more tire choices in my current size from Tirerack.com.

 

Stock 16" is 215/55. A good narrower size for winter tires would be 205/60 rather than 205/55 - keeps the load rating higher, very slightly taller than stock.

 

Skinnier would be better. Think of it like a guy with a peg leg and a guy with snow shoes. The skinny peg leg puts more pressure on the area where the peg touches the snow and thus punches through the snow. The guy with snow shoes walks on top of the snow and never gets his feet down to the ground below. You want to cut into the snow rather than ride along on top of it.

 

I only get one choice for 205/60 on Tirerack.com; and it's not a very good tire at all. So it would seem like the 205/55 is the best choice for now.