Is your delay used in a "set-it-and-forget-it" mode, or do you mess with it a lot? If the former, pretty much any delay pedal would do what you need. In the latter case, unless you're looking for exotic delays combined with modulation, I'd probably go for the MXR of the three you mentioned.
If you mess with the delay settings a lot and you might like to mess around with the fancier stuff, the Flashback is the only one on your list that can do all that. However, I would recommend against the Flashback mini (which I own) since with that pedal you cannot switch delay styles or toneprints from the pedal - you have to either connect to a computer via USB or "beam" predefined toneprints from a phone. The normal-size Flashback II would be a better choice. It has an array of built-in styles plus three user-selected toneprints available via a selector knob right on the pedal, and it is still a lot smaller than your Line 6.