I have the black with the rose and love them...so comfortable and look beautiful. I wanted a plain black pair and coveted the black sling back as something a bit different and finally ordered them a month ago. They are super comfortable as well and the strap feels perfect, not too tight, and yes, a bit more secure than the strapless. To my surprise, I ended up sending them back. After comparing them to my rose princetowns,I felt for me the strapless was more flattering and better for this time of year. I think I would like them better going into fall.
I do understand your lifestyle situation but feel both styles are instantly comfortable and stay on well. You can't go wrong and will really enjoy any pair!
PS I ordered the black with the fur to change things up ( I also have the blue blooms, LOVE them, and the new flora, both so cute and summery) and can't wait to get them next month...never thought I would order them ( thought the fur might be a bit much for me) but I am now such a
Gucci princetown fan!