I am going to throw another twist in here.... I have 3 sets of back mount doubles, HP120's, HP100's, a LP50's. I also have dive rites Nomad in sidemount with twin AL80's, In conjunction, I also sling a AL30 for class when I have students. Like ajtoady stated, different tools for different jobs. Personally, I prefer back mounted doubles. I do a lot of solo diving and slinging a pony all the time drives me crazy (personal preference) Both sets of my big and bigger doubles....Well just that too big for a simple solo rec dive. 2 months ago I purchased (after a lot of homework, talking to others Tbone thank you, I made the investment on the LP50's. I coudn't be happier!!!!! Small, compact, close to same weight as a single AL80, easier then carrying a pony, true redundancy, balanced, trim out Like the big doubles, same configuration, so I can stay proficient with my tech set up. I still can easily practice swapping regs every 500 psi, like the sidemount. More gas with me then an AL80 without any extras, over fill a little and same amount of gas as AL80 with a slung pony, still in a simple package. Trans fill onsite with the same AL80's you were gonna bring for a 2 tank dive.
I have owned the mini "Dubs" now for almost 2 months. I have over 150 dives in just them alone (yes I dive almost daily) I love them!!!!
Now diving is supposed to be fun ( I am gonna paraphrase Tbone here) Its your dive! As long as its safe, and you enjoy it, then dive your dive with what you want.