If you are given an option to mine 2 different coins for a whole year under free electricity, no payment or bills for that single year and then leave after what coins will you mine with 500MH? 250MH on one and the other 250MH on the second, this doesn't include Ethereum.
For the sake of giving you an answer you want, I would probably choose Monero and Ravencoin. I think Monero has a strong support base and will likely stick around for a while, even if it won't get mouth watering returns promised by some others. Ravencoin I think could benefit greatly if ETH 2.0 comes to pass. It's one of the most profitable GPU minable coins and will likely have a lot of hashrate thrown it's way soon.
Realistically though, I would use a service like Nicehash and get paid out in BTC to hold onto, or if I had to hold and altcoin, it would probably be Ethereum.
Choosing Raven coin is a good idea since it follows BTC in price action just like NEO but mining Ravencoin in a bear market isn't that great because Ravencoin takes more electricity than mining any other coins in the space right now, Ravencoin needs to be profitable like ETH when ETH merge is finally live.
Once it's profitable then that means the price has already skyrocketed (given the coming wave of increased difficulty that will surely hit after the ETH 2.0 migration). By then it will be too late to start building a stack. Sure, if you're mining on Nicehash it doesn't matter, but if you're trying to front run what is coming down the line, you'd need to be buying/mining and holding ravencoin BEFORE the price goes sky high. I wouldn't want to be stacking it once it's profitable, that's when the whales will be wanting to sell. Act like a whale, not their exit liquidity.
