I think a lot of the discussion in this thread is fine, but I think there are a few key nuances that get glossed over.
Look, there are so many options for 3 color lands, there's no shortage of choice. But it's not just about your 3 colors.
Your decks fixing/ramp package plays a huge role, and cannot be ignored.
Are you playing mana rocks? Are you playing green ramp spells? The lands in your deck are only part of your manabase, and if you don't pay attention to the interactions between them and the synergies with the rest of your deck, you are doing yourself a disservice.
Your deck is unlikely to be evenly split between the 3 colors, and your mana base should be balanced accordingly.
My 3 color Korvold deck has interesting tensions.
Green is obviously my most important color, for 2 reasons:
A lot of my fixing is green. If I have access to green, I can get access to other colors.
My 1 drops skew heavily to green (6 green 1 drops, 1 black, 1 red - although the red spell and 1 of the green spells are unlikely to be used immediately even if they can be).
Black, while not as crucial as green, is more intensive. The needs are different. I don't need to hit my first
as fast as my first
, but I'll need to be able to generate
more than my need for
.
And while red is my least necessary color to produce, I care about having a mountain in play more than a forest or a swamp.
Play patterns and the cards in your deck can shift your manabases needs and wants.
If you are rocking landfall cards, that can shift what you are doing. Pushing an emphasis to fetchlands or other tricks that may not have been there before.
Recursion - or tutors can also push and pull in different directions.
Do you have enough basics for your cards that care (if you have cards that care). Should you run more basics in case of nonbasic hate? What utility lands interact with all the other stuff you are doing? There is no point in running
Reliquary Tower if you empty your hand and can't refill. What lands serve you best?
I find the process of building a manabase starts with a rough core of a deck. If you have a rough draft of the rest of your deck, you can begin to draft a manabase that's complimentary. Building your manabase first feels like building the engine before the vehicle. I'm no mechanic, but I'm pretty sure you are going to want to know if it's a tank or a sportscar or a tow truck or what before you pick out and customize the engine.