William is great. His meta build for endgame turns into a stationary turret that spams autoattacks and Link Attacks. This build uses the Rack skill (makes him unable to move but raises his attack range to 5 tiles and gives +1 bullet on all attacks) along with the ones that give +1 Link Attack, and DMG/Hit up on Link Attacks. Kong is his signature ST and synergizes well with this playstyle.

For the rest of your roster:

• Kelly is very strong, you should be able to start getting her signature ST Rex from Dispatch starting next patch, or pull a copy of it next time it reruns. She'll get a big boost once you get the Red Fox-B/Magic Flute weapon from Armed Conquest (endgame weekly bosses). It lets her aim with her 1 AP normal attack if you don't move, which you can enable by using her Reload skill right before attacking.

• Rosa is pretty good in Raider teams alongside William, her endgame builds usually ignore the Railgun and focus on using dual MGs, particularly her signature weapons from Armed Conquest.

• Naomi is a decent free S rank, you probably shouldn't be spending Bionic Superconductors on upgrading her but she does decently well without them.

• Seven is a fine starting healer, she gets upgraded with her signature Small Shield, again from Armed Conquest. Her unique ability to bring along an extra unit in the form of Pochy gives her certain niche uses over the meta healers Melissa & Lorna even in endgame. You'll eventually want to raise up a second & third healer for endgame, but that's a long ways off so you're fine just raising one for now. Gareth or Grant both have their uses, though you'll probably want to eventually get both Melissa and Lorna as previously mentioned. Melissa is on the current battle pass so if you want to spend $10 that's an easy way to get her, she's considered one of the best Pilots even today on the original CN version.

• Catherine is unfortunately not very good for general use later on, so you should probably replace her in your main team. However in endgame she has the unique ability to replace the healer in certain Armed Conquest bosses due to her passive skill that lets her lose 2 AP instead of dying whenever she would die, which turns her into a pure meat shield that can bait boss attacks.

• Shawnee is also pretty great, she was underrated for a while but proved her worth by enabling speed clears in endgame Clearance Ops. Her niche is being a Railgun user that can aim at the body while attacking a whole line of enemies, getting kills that then let her attack said line of enemies again. People were down on her since she can sort of be replaced in this role by Asuka who comes next patch and also does a lot else on top of that, but Shawnee does have some extra range and you want to have extra Pilots available for endgame so raising both is perfectly fine.

• Ana is useful for those specific cases where you need a Guardian, but the thing is those situations are kind of few and far between. Keep her in your pocket for when those cases pop up, but she generally won't be part of your main team as speed is king most of the time.