The key question is what you want to do with it. Somewhere around 600-800msec delay, there is a big shift in how people plan to use it. Below that, they aim for things like slapback, and ambience. Above that, and other things becme possible. So delay range has to be framed in the context of what you want/plan to do.
Then there is the analog/digital divide. Digital permits endless repeats without signal degradation (though some units try to build it in as an option), and also permits other sorts of "tricks" that analog doesn't do, such as reverse, and effects imposed on individual repeats.
Tap tempo is something that, personally, I've never really found a use for, though some folks depend on it for gigging purposes.
Modulation (adding a little wiggle to delay time) can be quite pleasing. How much control over modulation one wants/needs is up to you. Some pedals, like the MXR Carbon Copy, simply imlement an on/off button for it.