Take Cover is slightly slower than Crouch as it does several things in series
(1) Validate your selected hard cover spot with the server.
(2) Roll you into any selected spot / slide into selected spot if close
if that fails
So, at the minimum, Take Cover will add client server latency on top of your personal reaction time and default ability activation latency.
Both abilities offer the same benefit: If an object interrupts line of sight between you and an enemy, you gain cover benefits against the enemy.
For PvP specifically, where you need precise control of your character, I really recommend using Crouch (default: shift-f) over Take Cover. There's definitely cases where Take Cover is very useful (you can bridge large distances by rolling into cover), but when faced with fast moving enemies that know how to play line of sight or obstacles like The Pit's fires, you're better off and faster using Crouch. It may take a little bit to get used to using both effectively, but it definitely helps.
The cover system is one of the main ToR gameplay novelty. Use only the skill Crouch would be really disappointing. It is imperative to change the cover system. For more roll behind a natural cover and less shield. Because the shield doesn't add nothing to gameplay. I love the cover system before the shield skill. When we have to found a cover and to crouch behind, and not just crouch anywhere. Today, the cover system is juste like a buff, and it's unfortunate...
Maybe BW could change the take cover skill by a roll skill. We'll chose the destination with the mouse like an aoe and the skill would work if there is indeed a cover available in the selected area. At least the skill will not depend of our target (which is stupid right now ...) and in exchange we would have a cd on the shield so as not to abuse it.
(sorry for my bad english).