I have heard the Rega Elex-R at home on demo and to me it didn't seem to have the resolution I was after, but it was superb with rhythm, the bass was very solid and clean, a very "musical amp" and reasonably warm but not too warm.
I have not heard the Musical Fidelity in person but am told it is a nice amp, warm and fluid sounding like the Denon and very detailed, Rotel amps are good but can be a little lean sounding, personally I've never really gelled with the Rotel sound or the NAD come to that, I've always prefered a warmer more organic sound.
After home demoing the cambridge CX81, Rega Elex-r, a Naim Nait 5, Arcam SA20, and Denon PMA1600ne I settled on the Denon , it doesn't quite have the musicality of the Rega or the detail of the MF, but to me the Denon sounded warmer more natural and cleaner with more air and can really boogie when you turn up the wick (not as good for quiet listening though) I also liked that it had tone controls and a reasonable sounding DAC (it is actually better than reported) The Denon is a great amp if you don't like it too bright, it's one of the smoothest sounding amps I've ever heard period.
The NAD would be great if you listen a lot at high volumes as it has plenty of power. Not on your list but should be -the Roksan K3 would also be worth considering if you like your sound loud and textured, big wide soundstage with loads of power in reserve and in my opinion better than the NAD and Rotel.
There are some that say the Kef's are hard to drive, I'd say any of those amps you listed would be more than capable of driving them pretty loud if needed. Speaker /amp synergy is always very important so make sure you try and listen to at least 2 of the amps at home before deciding. I would start with the Rega and MF. The Rega likes a good warm up first.