I think Tennant's accent could improve with time -- it's noticeably bad with Rs and some vowel sounds, but I think he'd have gotten there eventually if "Rex" had been picked up. And apparently I am willing to forgive a shitty accent if I can watch him being pretty.

Glenister's ... I don't think any amount of time would have helped that. I've never heard anyone who managed to sound like he was from all fifty states before. It was colossally bad.