a 3-way or triaxial is usually brighter, with more treble. a 3 way is best for use in front doors or dash, whereas a 2 way is better for rear speakers or fronts if you don't want a very bright front stage.
3-way just basically has 2 tweeters, or a tweeter and super-tweeter mounted over the midrange cone, whereas a 2 way has one tweeter mounted over the midrange cone.
I dropped my stock and got a 2 way co-ax for my front stage powered off of a brand new Alpine 9831. Just like the Glass-Man pointed out, they're not bright. They produce some pretty good mid-bass but the higher frequencies are just not there. Which made it seem like my music lacked clarity. Would have been better off havin a 3way up front
