I want to build my wife a very silly naya cats deck where every spell in the 98 can trigger Katarina when you pick a letter, and I guess I just want to ask which letter would be best. L has the most cats in mono-W, S has the most cats in Naya, but a lot of them are just bad common fodder. S gives access to the swords, though, so that one is currently pulling ahead. Help please! I don't have a decklist yet, I'm looking for which letter to use first. Also, I'd like to avoid as many non-cat creatures as possible.
Well, I went ahead and built it. If we ever play this deck, it'll likely be proxied, I don't feel like shilling out this much for the list, honestly, but it was a fun exercise
I think if you are committed to the bit, I think you more or less have to go "S". "S" buys you the largest volume of Cats to make a functional deck. It's also a way to run Swords equipment, Swords to Plowshares, Sol Ring, Skyshroud Claim, and other ramp and glue for the deck.
In any Magic set, S is the most common starting letter. I used to sell singles, and you'd need space for at least two if not three piles of S when sorting a new set compared to every other letter just having the one pile across six boxes.