OvationHost offers you a choice in webmail programs. You can pick whichever one you are most familiar with, or the one you learn to like over time.
You can switch webmail programs as much as you like, and you will still see all your emails.
We use RoundCube, Squirrelmail and horde for our webmail programs.
Don't forget, you can change webmail programs anytime, and you will still see the same emails.