1 Handle vs. 2 Handles

I think it's hard to say for sure b/c there are so many variables (skin, structure, size, etc.) that could make one bag look more formal or not, but if I had to pick, I would say that the single-handle is a bit more dressy. Of course my immediate frame of reference is the Kelly vs. the Birkin, Bolide or Plume, but I do think that single-handle bags (excluding shoulder bags) are more formal and dressy than two handles because it's a bit more streamlined and elegant and reminds me of vintage bags. When I think of dual-handled bags I think of in terms of hand-held totes which lend themselves to more practical, casual and daily wear.
 
one handle versus 2 handle is a very interesting thing to think about. not just for formal vs. casual, but just in general, pros and cons, the appeal of either, etc.
what keeps me focussed on the kelly vs. the bolide, one of the things, is the single handle. i am very drawn to the look of the twilly wrapped around the handle (where it covers it entirely) as a way to bring variety to the bag, really change its appearance, and i would not do this with a double-handle bag.