I'm a Deere fan, but Exmarks have a great rep, and are the number one brand around here (though it suprises me because they are also the most expensive brand around here.
Exmarks lay down an excellent cut, but no where near as good as the Deere's 7 Iron when it's wet, or the grass is long and lush. In dry conditions, they are about the same. I'd take the 925 over either the Exmark, or the 757. The new 900's are pretty darn good.