What criteria do you use for selecting which income tokens etc to purchase?

Well, the first thing I'd say are ones that have a solid project and team, with ongoing development, and good community support.

For dividend-paying tokens, I focus first on those that pay in a good array of tokens that I can use to reinvest via delegating to the Hive-Engine-token curation accounts, and some tokens that I can sell, to then buy more income tokens. I'm doing this now with the INDEX token.

For miner tokens, I focus first on those that mine tokens that I already use in delegating to the Hive-Engine-token curation accounts, which increases income there more quickly.

Do you have an idea for a contest or challenge that combines your suggestion with people building achieving the HP goals?

Well, I'm basically reinvesting all profit back into re-delegating and buying more income tokens, because I'm still building good passive income system flow. I have not yet converted any of it into HIVE or HBD, but that can be done at any time, which does connect my suggestion with people's HP/HBD goals. My end goal is to eventually be able to convert a good bit of the income into HP and HBD, to fuel long-term steady growth.

Challenge/Contest:

Research the various income tokens (dividend-paying and miner tokens) and Hive-Engine-token curation accounts (the Cartel Team, the LOLZ Team, Hive account@meowcurator, Hive account@aliveandthriving, etc), then draw up the plans for a reciprocal growth system, where the payouts from two (or more) components in the system can be fed into the other(s), with effect mutual exponential growth. Once you have a good grasp on how it would work, implement it. It doesn't have to be complex, but it does need to be functional. Perhaps give a prediction for when income from the system could potentially be diverted to convert to HIVE or HBD (some tokens pay in Hive too, of course) . The individual with the most efficient and elegant system wins (EDSMM prizes?).