There is no one best docking station -- the answer depends on what you plan to connect to it, and on what your budget is.

For basic keyboard-monitor-network connections, a simple port replicator (USB) is fine.

For more demanding external peripherals, particularly high resolution external display(s), you'll want a thunderbolt dock.

Yes, I assume that I want a thunderbolt dock. No budget concerns.  I plan to connect two 28" 4K monitors. Which one? 

The one below should work, depending on the interfaces your monitors have.

https://www.dell.com/en-us/work/shop/dell-thunderbolt-dock-wd19tbs/apd/210-azbi/pc-accessories

What about this model? 

https://www.dell.com/en-us/work/shop/dell-thunderbolt-dock-wd22tb4/apd/210-bdqh/pc-accessories

Yes, I noticed that.  Thanks!

How do you know what spec to look for in comparison to 'more demanding peripherals'?

I have a dell WTB19TB (with the above laptop model).

In terms of connected peripherals, I have 2x Dell S2721HS monitors (1 in the display port and one in an hdmi :S), a webcam and a wireless keyboard (ok and a network cable, probably not relevant)

Quite frequently, the computer locks up. completely, monitors just freeze and nothing but a hard reset will revive it. If the laptop monitor is also on, it happens every day. I wonder if this is a symptom of a non suitable (or faulty) docking station