Most trimmer heads in my experience accept .105, even the generic Speed-feed clone I bought off E-bay.
As far as string line goes, I err on the side of smaller is better. I've found 0.080 to be the best all around use for me and I have plenty of chain-link to cover.
The .080 will go through more string doing something like a chain-link fence line or heavy/tall growth, but it throws a lot less dirt and debris in your face (and at other things) when you miss the mark, and is less damaging to the stuff that you don't want to trim that you hit on accident, or when you're in a hurry. It's also far more effective on normal grass / trimming needs IMO and gives a cleaner cut. I even use 0.065 from time to time in areas that aren't heavy where I need to be careful.
.105 is like the Bazooka cannon for normal trimming. The only purpose it serves for me, is when I have to clear out overgrown fields with heavy stems / light brush, but you have to have a machine big enough to keep it spinning at high speed. I don't see the purpose in a small residential / suburban / city lot setting unless you are a glutton for punishment.
.095 is a good compromise if you have a single trimmer that needs to be a one-size-fits all.