I can only give you my personal opinion, and please do not take it an investment tip. I'm not a finance adviser and I'm risking my own money here, and I know I can lose it. For me I would go for bitcoin, it was the first one, it has a great team behind it, if has the biggest community, and it already has a lot of money invested in it. If BTC would fail right now, I think all the other coins would just follow it. In the future I don't know of course.
Also, from an evolution point of view, I think it has the most potential as well (lightning network, atomic swap, are just a few things that will probably come). As for the investment itself, I would see it as a long term investment. Buy what you can and then just hold them. If you are a good trader, I think any coin will do actually, but for holding I would go for BTC.