I was always told to avoid the MF 27/29/31 combines. They are of a monocoque design rather than having a chassis, and in the long term this leads to fatigue in a lot of parts which need the rigidity. On the plus side they are cheap to buy, and you will always find some machines which have been very reliable for people, there just don’t seem to be many of them!
I like the 32/34/36 range. Only drawback is that the electronics are built in, you can’t just switch off a monitor and carry on like an older machine when something electrical goes wrong. I nearly bought a MF26 a few months ago. That looked ideal, simple and basic. Not many of them about though.