The crew doors are interlocked slam doors with inflatable air tight portal seals. The saloon doors are a sliding pocket type, forced against a soft portal seal by four actuators, once the train passes the low speed threshold.
Of the stock I have previously worked on;
14x - the doors do the job, but have lots of issues with settling and they wear out fairly quickly compared to others. If they are opened/closed on low air pressure they don't lock, despite appearing to.
150 - good, simple above door mechanism, one ram, one adjuster for the local door, one regulator for the saloon. Limited obstacle detection, but very rugged. Until the bottom runners snap or the pockets get a bit mucky and need cleaning out...
153 - fine, although over complicated, with far too many microswitches. There's one switch that will close the door with no detection, which apparently hurts a lot when you are testing according to one of my colleagues.
158 - far too over complicated, rarely understood well. If you have any problems past centre over locking pressure, you may as well give up now - the four hard stops and four turnbuckles per door leaf require a huge amount of patience to get right. If in doubt, don't change components, ignore your modern VMI, set it up to the BREL manual then test to the modern spec to check. 14x and 158 always seem to get themselves out of sync, no-one cares why, open and close them all to fix!
HST - simple to check but theres a fair degree of measuring and testing the latches as per any other mk2/3 door, nothing complicated, even CDL once you understand it isn't too scary.