Stability, performance, price.
I would say a mix between performance, stability, managebility, functionality, flexibility, compatibility and price.
I'm all into SDN, automation and integration.
We avoid proprietary protocols and try to achieve vendor independency.
Also: know the vendor's architecture & vision.
ARCHITECTURE AND PERFORMANCE
I really enjoy the Meraki's approach to switch administration and I think all future switches (managed locally on primes or via the cloud) should provide administrators more visibility and ease of administration.
For me there are several: Is the switch L3, does it have CLI or some management, and I think I would prefer a CISCO with gigabit connectivity.
There are several variables to verify, but one of them is that the switch have to be manageability and VLAN compatible.
Relatively new to Distributed systems but it has to be rock solid, easy to use and maintain.
There is no one uber criteria for all types of switches. It always depends..
Campus access switches require PoE and stack capabilities. DC access switches have to be superfast and reliable. Core/Disrribution/Spine and DCI role switches are to support extended L3 and MPLS functionalty and so on.
Nevertheless in a new era of SDN where automation and orchestration paradigms come to play all ongoing switches have to have some sort of open API. Besides that an interoperability is a key factor as well. So open standarts is my another main criteria.
I don't think there is only one important criteria, it should be a balance of price, performance, features, manageability and support.
My most important criteria in Ethernet Switches would be compatibility of needed functions (hardware and software used) and other products, throughput, reliability, and the accountability of the product to be functioning for 7-10 years (the next renovation/purchase cycle) with-holding the ability to comply with the emerging technologies. Also the company's support (manufacturer and supplier) will also be crucial...
PoE capacity to port ratio comes first. And of course the uplink bandwidth capacity. I don't look at anything other than Cisco. They are #1 for a reason, and it is my personal experience that I can place a Cisco switch, configure it, and forget it. They just work.
Number of ports, PoE, processing, and look for a product with good reviews and customer service~
I look for proven reliability i.e., Cisco. There's a reason they are the go-to industry standard for switching. As far as features, I look for Gigabit Ethernet ports all around, PoE, and Stack-wise capability in order to future-proof my purchases for as long as possible.
Depending on what your requirements are my opinion is throughput and functionality. Management is another consideration as it won't do you any good if you can't manage the switches purchased. As far as POE is concerned look at the wattage and make sure your devices are going to have the power needed. The rest of the lights, bells and whistles are up to you.