Hello!
I haven't listened to the Sonatas but know Triangle's (for about 5 years now) and I am a great Fan of them. What I have listened to are the Dynaudios. I completely prefere the Triangles to the Dynaudio's. I wan't tell which one are better because they sound diferrent. You need to hear both speakers in a good setup and find out which suits you better.
Triangle's are great allrounders with a boogie and fun factor that's hard to resist and when live music comes into play the Triangles are very hard to beat... So some speakers look bland in comparison. And not to forget Triangles benefit greatly from tube-amps!
Trust your Ears and listen to your heart.
Cheers!