I prefer ICO's with an already working product. For suggestions of such projects you can check the following thread: https://bitcointalk.org/index.php?topic=2451482.0

Also, make sure to do your due diligence, read the whitepaper, check ICO review sites as well as forum threads. Scammy projects are getting better and better on making the projects seem legit so we need to be very careful when choosing projects to invest our hard earned coins in.