I’d definitely go with PowerBlock. Been using them with clients for over 3 years. Just bought the add-on to go to 70 pounds each and they are still sized well enough to use comfortably without sacrificing appropriate technique.
I like the Bowflex as well, but as you go up in weight I believe the do become a bit too long to maintain proper technique with a lot of exercises.
All about personal preference and how you will use them with clients, however.