Okay, I'll agree that an Spriest/lock combo is good... but don't act like it's the end-all be-all.
We have a number of tools to combat anything a spriest or lock can throw at us. In fact, while locks are a tough fight I've never had a problem with an equal-level shadow priest. Fear? Oh, silencing shot. Or, if you're BM, Bestial Wrath/tBW. If the pet doesn't kill you, the hunter certainly will.
As for locks, they are more difficult for me as a MM, but again... use silence, wail away... kite at range (to stay out of DC radius) with conc shot and wear them down. You've got FD to get the pet off of you, and an array of almost instantaneous shots that will bring pain to that 10k HP. We've got longer range, and as long as we can stay there... it becomes easier to wear them down. Or break fear/DC with trinket, scatter shot, snake-trap (or freezing trap, aimed multi arcane). Yes, they're a difficult fight, but it can be done.
To the OP, roll what you think you'll like the most. Shammies are a ton of fun and very powerful, but it also depends on your spec. EX: I take enhancement shammies easily. Elementals are a bit more difficult. :)