Finally a hard hitting question!
I think I have to go with the original Halo. There was the pistol, just such an iconic weapon that was fun to play with. Played so many hours at my friends house I eventually went and bought an xbox myself. Indestructible vehicles meant you could do some pretty crazy things with them in campaign. Just a shame it wasn’t on xbox live.
Had a lot of love for halo 2 but I think a lot of that is also that was still the golden age of xbox live. Before party chats so you had people actually communicating while playing, and before things got too toxic where you didn’t even want to have public voice chat on. I know a lot of people didn’t like dual wielding but I found a bunch of ways to make it work, and didn’t hate it.
The later halos kinda blend together. Whichever one had the mantis was great though, would play with friends and grab the one at our spawn and then go rush the other side and just control the map with both of them. Also liked the gauss warthog, my friend was a great driver, and I got some crazy streaks with that cannon.
Haven’t played halo 5 as I don’t have an xbox one.