Okay, no I haven't. I've been looking up the difference between alpacas and llamas. I thought I would know instinctively, but I guess I don't know my even-toed ungulates as well as I thought.
Size: Alpacas are small. Llamas are large.
Face: Llamas got the long face. Lamentably long, is how I'll remember that.
Hair: Alpacas have shaggy hair that is finer than llama hair, and makes really nice wool. So when in doubt, I'll make a sweater out of the hair and the nicer one is probably the alpaca.
(Besides the alpaca and the llama, there are two other extant lamoids: the guanaco and the vicuña. I'm sleepy so I'm not going to try to think of mnemonic devices for telling them apart. I'll leave that problem for future, South American Guillermo to figure out.)