I run and S210, never had a S214 so not the best qualified, but do read on.
I LOVE the 124 and really, really want one. However, the question is 'what do you prefer?'.
Nowadays there's not a lot of time to muck about with a car (much as that may be enjoyable) nor a lot of money to sink into one. A common need is for a huge estate (hence 'S' rather than 'W') which requires little time or money.
While I really admire the 124s and not even notice 210s (despite having one) the 210 has much going for it. It is a total barge, swoops along in silence and is a refined thing that one might look forward to using. Auto wiper, decent speakers, really hardy interior and tighter than expected handling etc are all attractive and the Avant Garde versions can be an attractive looker.
Wth a 210 there's the inevitable need to keep up with the rust, but that will be needed at least as much with an old 124, perhaps more plus keeping up with tons more stuff like seized nuts and bolts, in-depth rot, corroded brakes etc etc likely on even the best 124.
Collectors car in which to pose, enjoy, tinker and improve, a 124 may be preferred above most cars in the world let alone a 210.
Everyday user, cheap, disposable, vast and relatively inexpensive to run and a superb drive to boot is there anything better than a 210? They are so cheap and plentiful that when the inevitable happens, £200 or so for scrap is a major contribution to the paltry cost of the next one. This suits me, and despite my jealous looks at a passing S124, this is what I prefer.