Database connection pooling, should we pre-warm it or just grab a connection when we need it?

hey folks, i'm thinking about how to handle database connections for a new service. we could get a bunch of connections ready when it starts up, which would make the first few requests super fast. but, if the load is unpredictable, that might just waste resources sitting around doing nothing. or, we could just make connections as needed. that's better for resources, but the very first request might be a tiny bit slower. what have you guys found works best, or what do you prefer? anything i'm missing