I like to get fatty beef, lean lamb, and pork belly. You want these sliced as thinly as possible, so make an extra run to a Chinese or Japanese grocery store, where they sell these meats pre-sliced. The thinner the meat, the faster it will cook; really, each slice should only take one or two swishes in the boiling soup. Try holding on to them with your chopsticks, only letting go for a second to cook thoroughly, but avoid losing them in the bubbling pot. If you must, you can also get those little nets for hot pot noobs.