None of them, I'm just focusing on Kama Summer, and I don't miss the opportunity and I don't want to end up like it happened last year, in September.

Skadi, for the option of double and triple Skadi going forward.

Skadi is useful, but do you have many servants that she works well with? Like Dantes, Summer Okita Alter, Parvati, etc, along with the CEs? I've taken to using her for looping regularly farming nodes when I can. More challenging battles get the more useful Caster Artoria who offers a lot more utility.

Gilgamesh can be a good Buster looper, given his Anti servant niche covers so many of them. He isn't a favourite of mine, but he would do the job.

Only Achilles

Well, I won't say you shouldn't roll for her, she just won't have much to do.

There is also Taigong Wang, but with the arrival of Achilles, I only use him to increase the power of Achilles' Quick Cards.

Do you have Summer Yu, Santa Karna, or Kiichi Hogen?

I always recommend gathering meta supports, and as a result I'm a little slim on DPS servants.😅

Realistically, if your roster is buster-oriented, and especially if you have Koyanskaya of Light, Gilgamesh might be the better option. You just never know when a good Quick servant might spook you.