I think @viridian covered it pretty well. I appreciate the ST-70 design but most of the original units sound pretty noisy, by today's standards. Especially the user-built kit amps. The new ST-70 clones can sound pretty good but they have a specific sound that you will either love or hate. You will want to this ampo with fairly sensitive 8 or 16 ohm speakers.
In the same vein I love the build quality of the MC275 but it's not my favorite Mac tube amp. Yes, the new reissues do sound quite a bit different than the originals. But it's a great amp for somewhat efficient 4 ohm speakers.
To my ears and with 8 ohm speakers the used (old school) MC225 and MC240 are more enjoyable than either the units you mention. But that's me. YMMV