For an idea exchange platforms the following should be look on:
1.Security. The first thing I do look on in any exchanges that I want to transfer fund in is how secure it is.  Many investors has lost their investments capitals through unsecured exchange . If you are an investors then security should be your first concern.
2. Volume: You need to know and compared the volume because it creates liquidity.  I do buy some coins and at the end cannot sell them because of low volume.  I prefer binance and hitbtc because of volume.
3. Fees.  The fees should also be one of the things you should look on to before investing.  Many exchange especially the old one still retain they trading fees and this do affects the cost of trading.
4.Rate at coins marketcap.  I also look at the rate of exchange platforms on coins marketcap. This enabled me to be able to know the performance of those exchange over time.
Investments, is very risky and you should not go into it without adequate knowledge on how trading work and how to trade profitabily.