I have only played Wizardry VII extensive and though I recall it quite fondly I don't have enough memories to judge the gameplay or compare it with M&M besides both being first person perspective, but party based rpgs.

OTOH the Might and Magic series is one of my favorite rpg series. I have started with M&M III, which was quite amusing at the time. I have bought the M&M 6-pack here on gog to dip into memories a bit and maybe finally play 4+5 which I missed back in the day (and I also couldn't resist the Wizardry discount :-)).
M&M 6-8 are good RPGs in my book, I have played all of them several times and just started a couple of days ago with 6 again.
When they came out they had already slightly dated graphics compared with other games of the time, but they are enjoyable still.
There is not much interaction like there is in the Baldur's Gate series; you have only few choices when talking with other people; most of the dialog is general hints or about quests.
M&M ist basically hack & slay with buffing up your party members, but the respective game worlds are large and colorful and mostly free to roam. You get your quests and can do them in any order you like.
M&M has a skill system where you have to buy guild memberships and skills and put the points you get on level-up into these skills. To acquire expertise, mastership and even grandmastership you have to find appropriate teachers who teach the rank against gold; grandmastership requires certain premises like appropriate class, certain stat values, and a special task for each profession.
Almost forgot: In the later games alchemy is a useful skill, you can brew permanent stat boosting potions (with the appropriate skill and rank).
Lots of monster hordes are lurking everywhere.
The series has an automap feature from part II on whereas an automap feature in the wizardry series was only introduced whith Wizardry Gold.
Part VII was unique because late in the game you had to decide whether to take the path of light or darkness. Part VIII was unique in another way because you have to hire your party members (and also can fire them); there are new classes and races avalilable, e. g. vampire, dragon, minotaur.

I liked the music especially in part VI, it has some beutiful themes in it which where also used in HoMM III.

I have never played IX, because I couldn't ge used to it.

Overall I would say I recollect Wizardry as a bit more sophisticated and M&M as more straight forward. Both series have some scifi elements included.

Yes, me too... :) Because of it I started this topic - now I have both renowned series and I can't decide which one I should start first...:)
I read about complexity and vastness of Wizardry games. So maybe M&M would suit me better - you know, still there's job, family and other unnecessary things... :)

Wizardry VI and VII are two of the best RPG's ever created. Might and Magic VI was a great return for the series and spawned VII and VIII which were also good games. If you can get past the graphics in Wizardry VI and VII I would say go with that series. Although I would not miss out on Might and Magic either.

I've finished Wizardry 7 once years ago (didn't have 6), but I probably won't do this again due to its massive size. I spent sooo much hours training a party that could conquer the gorrors... 8 however is one of my favorite rpg from the past and I've finished it lots of times with different parties and mods. Soo, if you don't have a lot of time I suggest stick with M&M and Wiz 8.