I agree that you need to do your own homework on the coins you want to invest in. You also need to know your investment goals. Do you want to buy a coin cheap now and then sell it all for much higher in two years so that you can go on vacation or buy a house? Or, do you want to find a way to earn a passive income?
If you're looking to buy low and hold and then sell high, then you want to find a very good coin that hasn't yet been discovered and buy it now.
If you're looking for a passive or residual income, you can look for the decent proof of stake coins.
I certainly have my favorite coins but I'm not going to list them here because even though I believe in them I wouldn't want you to buy them blind. However, you can look through my posts and get a pretty good idea if you're willing to take the time
Here are some general things to look for in a coin:
1. professionalism. Do their devs treat people in their community and inquirers with respect and courtesy?
2. community. Is there a community? You really don't want to get into a coin that doesn't have a community.
3. more than one developer, a good development team. If it's a one man show, skip it. Look for a solid team developing the coin.
4. solid plan. make sure it's realistic what they plan to accomplish. Read the intro post and white paper and ask a lot of questions, which will also help you figure out number 1.
5. incentive to hold the coin. There needs to be some very good reasons to hold the coin. For example, some coins will offer rewards to holders. Proof of Stake coins reward holding over selling.
6. supporting infrastructure to add value. There has to be more than just a coin. Anything that can support or add value to the coin.
7. market support. Nothing artificial but simply good reasons to buy the coin and support the price, such as a bounty system that pays out in the coin.
I hope others here have some good recommendations as far as what makes a good coin. Please add them here, as I'm sure that would help lots of people.