The biggest marketing budget has potentially the largest growth potential.
If you have a good product but not enough money to peomote it, you will likely fail.
If you have a medium quality product but a huge marketing budege, your change to succeed is unlike higher.
We no longer live in a product driven world (whether or not that is good thing is your call) but this means that marketing is or will become a huge part of these alt coins. So many of these coins have a solid team, have well written code, and offer a working product, but nowadays that isn't enough. Marketing is becoming a part of the larger ICOs because an effective campaign can generate so much more interest than the product alone. Now that some of the general public who aren't tech experts are getting into bitcoin and other altcoins, I see marketing becoming more and more important.
Still look for: A solid team, advisers who have been on successful projects, a well written white paper, coins that will be able to be incorporated back into the ecosystems they are created for (i.e. wont be created just to be flipped), but also consider the coins who have marketing teams/ budgets that will get more users involved and make you ICO investors more $$$