Blue
Ravenous Bugblatter Beast of Traal
Two characters playing summoner-focused spellcasters could also really annoy the rest of the table because their turns are going to take longer too. But again, that can be mitigated with good coordination. They can share resources/summoned creature stat blocks and streamline their play.
House rule: If you're a summoner, have multiple printouts of common summons. When you summon them, give them out to the other players to run. (Or with online games having the link to the SRD would be a suitable alternative for creatures in it.)