In terms of volume, Vortex is easily the largest company in the world right now. Leupold used to be, but that was a few years ago. Now, Vortex has a bit more than double the revenue of Leupold.
I am not exactly sure who else is in the top five, but I would guess Bushnell. Not sure about Zeiss and Nikon. The fastest market share growth is likely Sig.
The fact that Vortex is the largest right now is not real important by and large. What is important is how quickly this stuff can change even in a fairly mature and saturated market like sporting optics.
On to the original question: both are good scopes. I prefer Mark 5 weight and Razor HD reticles.
If you are looking for a compact scope, go with the Mark 5 3.5-18x44. I liked it a lot.
If you are looking for something with more than 20x of magnification, I would really consider the Vortex AMG 6-24x50 as well.
ILya