I use both. I like to bulk age with the one on the left as there is less evaporation in those, as well as less chance to have a pressure change send the liquid from the lock into the carboy. I use the one on the right during heavy secondary fermentations because if there is overflow, it is MUCH easier to clean.
Here's a cleaning tip for the bubbler though: When you are cleaning your carboys using a jet off the sink, like a bottle cleaner, you can also shoot water through the bubbler which cleans it pretty good, but you have to be careful or you shoot water everywhere.