Definitely plain navy or plain grey/charcoal. And stay away from peak lapels if it's your first suit.
My recommendation in order of importance:
1. Plain navy
2. Plain grey/charcoal
4. Window pane
Non-staples but fun to own/wear
5. Chalk stripes
6. Peak lapels
Thanks a lot for your advice. So I'll focus on a navy or grey/charcoal suit. Which one would you prefer? Both colors are fine for business of course, but some people say navy is better for the first suit and others say you should go for charcoal. What are the pros and cons of the colors? I have really dark hair and a pretty pale skin color if it's relevant.