Questions about how to choose a switch

I'm looking for some assistance on some guidelines on metrics that I should be looking at when choosing a network switch.

I've read on this subreddit about buffer sizes, switching fabrics and a few more statistics. I'm looking for something outlining the key stats that I should be looking at when choosing a switch and what their impact is on the performance on the network.

I work for a company that installs voip phone systems and I'd like to know better what I should be looking at when selling switches.

Ideally, if you have any knowledge of courses I can take or resources to better learn about choosing which switch to use and better understanding of switch hardware and the performance advantages between different hardware I'd love to start reading away.

​

I appreciate you reading my post and look forward to your responses.

​

Thanks!!