I prefer a token already in exchange for some reasons:
There's no need to worry if the project I'm investing with could be listed in the market.
The reputation of exchanger of that token project can certainly help for it to be successful (specially if it has more users than any other exchanges).
You won't guess what price of your token will be so much since it's already in the market.
It's very practical since we all know that a lot of project in 2018 doesn't get listed in the market, causing a lot of loss to investors.
Reasonable reason. I also tend to choose bounty projects with tokens that are already listed on the exchange. It increased my enthusiasm and confidence in supporting the project. Even though it's not a guarantee because drama can always happen. Allocations are deducted, rewards are not distributed, etc. But at least we must always be optimistic and do our best.