Which amp would you go with

I had the Musical Fidelity M3 which is basically the
M2si and it's a fine amp. The build quality on it is
excellent and it's more powerful than the numbers
would suggest. 

Well I am going to have to chime in on this one as I have the Vincent SV-500.

I have had it for about a little over half a year so far and love it. Connected to Martin Logan Motion 40’s and since they are 4 ohm speakers, the Vincent (according to their specs) should be pushing close to 80 wpc. Also connected to it is a Questyle DAC CMA 400i, Denon Universal Bluray Player for CD playback and a Denon dpf-300 TT with a SimAudio 110lp v2, Denon Cassette Deck.

All I can say is that I am loving everything. When I first got it I was afraid it would not have enough power for Logan’s but wow, I do not even need to turn up the volume very high to get good music to my ears.

I really wanted the big brother, SV-237MK but it was out of my budget and so took a chance on the SV-500.

I recently added a Isotek Evo3 Sirius Conditioner and High Fidelity Cables MC-0.5 to the system plus Audioquest Power Cables to the Vincent and Dac. I feel it has definitely added some impact overall, deeper bass and bigger sound-stage (holy crap, am I talking audiophile language now, haha).

Anyways, I can vouch for this Integrated but I am sure the other one’s you are considering are awesome too. I do not feel the need to do any tube rolling as I am quite content with my setup so far.

The only other thing I want to upgrade eventually is my TT and upgrade to a dedicated CD Player or Transport.

So that has been my experience.

If you're open to second hand, consider a Vincent SV 237 (not the MK).  I picked one up recently for just a little over $1K and am very happy with it. Other integrateds I've owned include the Peachtree Grand X1, Peachtree Nova 300, Heed Elixir, and Audio Research VSi55. Only the ARC is as good in terms of sound quality. 

The Croft is as British as can be and is magic. Also consider an LFD

I just recently acquired an Arcam sr250 which I believe has a very similar if not the same internal amplifier as the SA20 integrated. It does a great job with my Revel F208 towers. The class G Arcams are heavily class A weighted (the first 20 watts on my SR250) and its apparent. 

I have never heard Rega or Vincent amps but I love my Rega turntable and I previously had a Vincent phono stage that was great for the price point. The Vincent phono stage sounded and felt like it should have been much more expensive. 

Just my two cents. Good luck on your quest!