I've been wondering for a while which would be better some people say shinji needs alot of stones and some say komamura needs a lot of stones and they're both good I think so it'll help out with a bit of help
shinji is good if you want a team fully focused on attack but to use him to full affect you need a zanpaktou with a 0% damage rate boost or higher since most reduce your damage rate for vanguards.
Komamura on the other hand is a much more tanky tank than shinji who is squishy tank. he is focused more on defence and surviving hit rather than delivering them.
in he end I would say that Komamura would need less spirit stones than shinji or rather shinji would need the kind of spirit stones you want to put on your main and assaulters rather than your vanguard.