I prefer open-heel fins with boots, definitely! I started out with those in my OW classes, then managed to forget ONE fin on my very first dive trip! (I was checking if my fins would fit in a particular suitcase and forgot to take the "measuring" fin back out!) Unfortunately, the dive shop at my destination had only full-foot fins for rent. I wasn't a fan... they weren't as easy to put on or take off as my open-heel fins, and when we knelt in a sandy area to demonstrate OW skills, sand got inside both fins and started rubbing sore spots on my feet.
Besides, boots provide great traction on a wet boat deck and protection from rocks or other debris on the beach for shore dives.