Which Leo to keep?

While I'd say you could get QR3 by upgrading Subaki or Klein, you do you.
+res is just great for him and he doesn't need speed. Just make sure to refine his weapon if you ever use him.

Definitely +Res. Spd is a dump stat for him since it's already abysmal, where Res will up his tanking potential at range.

Keep +Res -Spd. He’ll appeciate the extra magic bulk and his speed is literal garbage already.