I'll vouch for the argon, they are a terrific bike.
The I almost bought a radon, but I came across a very good deal on something else.
as far as size goes. do yourself a favor and go to a shop to try the bikes out.
The argons do use a fairly standard geometry so the 58 might be a bit better fit, but at 17 you may still grow a bit.
where are you from? (greatly affects MSRP)