I have the Kaufman and would like to get the ROM guide this year. The ROM one is very useful for discussing food plants (realistically too! first guide that lists the weeds/alien invasives that get eaten so more realistic for urban butterflies) and for discussing larva. Kaufman uses drawings not photos which can help simplify what to look for in some cases. If you can, maybe take both out from the library first and look up species you already know to see if it feels helpful.