How big of groups already you getting when you raid. My raid groups are usually 15 or more people so it doesn't really matter what I use. A ttar, a couple of vaporeon and a rhydon are usually more than enough.
My point is, unless you are scraping by with the bare minimum players, don't waste your dust building up pokemon that are only useful for a specific task for a limited time.
Ttars with stone edge and golem with double rock I think would be best if trying to do it with a very small group.