There are generally two considerations for networking in your ESXi hosts, which is whether to use 1 Gbps or 10 Gbps NICs. You could always consider a 40-Gbps network as well. No matter what, you will always want to ensure that you have at least two multiport network cards to separate your traffic, which will allow the resilient network design that you require. Regarding the speed of the network that you require, this will depend on the VM LAN traffic within your infrastructure, and that completely depends on your use case.

If you are streaming a lot of HD media into your VDI desktops, then 10 or 40 Gbps may well be required. Whatever the case, ensure that you really understand the network requirements, as getting this wrong will result in a poor end user experience.