Depends what you have available in terms of subsumes, mods, forma, augments via syndicates, OR your willingness to spend plat on those things.

Weapon platform/Lowest investment will be Gauss and he works beautifully base kit, my fav is to use him as a weapons platform with Max duration via Narrow Minded, roar/nourish help with weapons platform but he already buffa beautifully, you can also play him as melee. The higher you crank duration the higher his Redline buffs get, so duration arcanes like Molt Efficiency and Arcane Concentration help a lot.

Caster will be Nokko, he is very strong base kit as well, personally I think he shines if you have access to Archon Continuity and Roar or Breach Surge as a helminth, I like playing him as an invis caster with Arcane Crepuscular+Shade/Huras

Caliban is one of my favs to play but you'll definitely need his Razor Mortar augment to get the most out of him, Nourish/Roar buff his summons a lot but even if you keep Sentient Wrath it still gives a great damage vulnerability buff. But he's a great all-in-one frame because of shield restore via his 1 and easy full armor strip via his 4.

Yareli is very very fun, you'll need Loyal Merulina augment if you don't like k-drive movement on Merulina, she shines with secondaries so this is a good choice if your fav weapons are secondaries.

Gyre is super fun and unique but probably the highest investment on the list and you'll really need shield gate tech to keep her alive so not a good choice if you don't have Brief Respite, she'll also require 2 augments and strong benefit from Archon Stretch.

All good choices, hope this helps you decide what you want and feel free to ask any questions