The safest way is to find a campaign that pays in btc (or ethereum, if such exist). This way you can know what kind of money you will receive. Unfirtunately, it is not the same with some icos. You'll probably get your payment in about a month and there's low probability the coin will make it to the market and pay off. Yet of course it is easier to find an altcoin campaign that a btc one, so I suggest you to look at their projects and choose the one which will soon finish its ico stage and has strong partners and community behind it. Good luck!