My recommendations :

Might and Magic 7 - Some will disagree but this one was IMO the best of the series. M&M 4 & 5 + 'Xeen' was great for it's time but can be a chore to get through these days unless you are just blinded by nostalgia. M&M 6 was a good reboot of the franchise but it's dungeons are long and often boring and the character creation and development pales in comparison to that of M&M 7(M&M 7 at least had a few different races to play, a few extra classes, a better skill system and the 'Arcomage' mini game which is worth the price of admission by itself!).

Heroes of Might and Magic 2 and 3 - Heroes 2 had outstanding 2D graphics with a bright palette, better music and in some ways better balance. Heroes 3 had the brilliant feature of both 'Might' and 'Magic' hero classes for each faction/town type(so instead of just a "Sorceress" as the 'woodlands/nature' hero, you had "Rangers"(might) and "Druids"(magic) for example) and also the random map generator(which made the game infinitely re-playable), lots of new items(combo-artifacts FTW!), units(probably 4 or 5 X as many as heroes 2). It suffered from some design flaws with the magic system(very many spells are completely worthless and no sane player would ever use them) and some of the names of creature upgrades and such as well as the horrible "Conflux" town/faction that was forced on us and rushed out the door due to a bunch of teenagers at the old Astral Wizard site complaining about the Warhammer 40k-ish "Forge" town that was planned).

Heroes 3 also had the 'wait' button which is a HUGE improvement over Heroes 2 in how combats play out.

Might and Magic 1-6 bundle - I would recommend this because A) you get 7 or 8 games for one low price and at least 2-3(most would say more I am sure) very good if not great games. None are as good as M&M 7 IMO but they are still well worth the price.

I am something of a completist so I picked up their Heroes IV bundle as well as their new Heroes V bundle(with the free "Assassin's Creed" which I have no interest in playing) but the only one of these I can really recommend someone else pay for and play is the Heroes of M&M V: Tribes of the East" game(included with the Heroes V bundle). Even with all the fixes and such for Heroes IV it is kind of lackluster compared to the other Heroes games.
Heroes Chronicles is something you will only want if you played through all the Heroes 3 campaigns and really want more of THAT. The Chronicles campaigns are well done for the most part but they are kind of a mixed bag. Many of the scenarios(most of them as far as I remember) are very small maps and if you will eventually be forced to play a campaign with a faction you don't like(for me it is the "Fortress" town/faction). Might and Magic 7(VII) had arcomage. M&M VIII had crappy 'races as classes' nonsense.