Well... in my opinion... the easier they are to get on and off the bike the better... so those with velcro straps can be a pain.
I had no intention of paying top dollar for ortleib bags, but they do tick most boxes... so spent a long time looking for a pair of bags which had an easy quick release catch system, were waterproof, looked like they wouldn't fall apart by next year and had largely positive reviews... having narrowed it down to a couple of options in the 20-25 quid each price range, I thought sod it, I'll spend the little extra and get the ortleib's at £64 a pair... the extra £7 a bag is money well spent.