As the subject states, I'm looking to find out which of the 8 games here on GoG would be the best to start with, gameplay and feature-wise.

I haven't played any of the series yet.

That depends.
If you're into older games (dos era) I propose start with 3 and progress with the numbers. (1 & 2 are for true hardcore old schoolers out there with nostalgia for apple II games etc.).
If you want something a little more modern start with 6 and then go with 7 & 8.
And skip Crusaders.

But these are jus my opinions, I'm sure there are people here who will tell different.

I recommend starting with Might and Magic 3. If it's too difficult for you start with World of Xeen instead.

Thanks for all the input, you lot. I'll get it on with MM3, then.

Wish me luck.

Remember that the GOG version comes with the cluebook as one of the extras in case you get stuck. Beware spoilers, obviously. I find the cluebooks very useful for looking up item stats as the games are not usually very informative about which items are better than others. If you search the PDF for the item in question you can avoid most spoilers, but the "true" way to play would be to not use the cluebook and identify items in-game.

I was an absolute beginner like you. I had never played any of the Might and Magic Games.

I started with III, and while I kind of liked it, it was a little too overwhelming. I just didn't really understand how to play it or what anything really meant, etc.

I have now switched to VI and love it. I have played it almost 20 hours and I just started playing it about 5 days ago. There is just more out there on the web and in the manual explaining the game and how it works.

Looking back at III, I think I am going to like it a lot better after VI because I am going to have a basic understanding of what the M&M universe is about. I like games like III, it was just too hard to begin with when the documentation for the game assumes you are already a D&D and M&M pro.