I have a friend that shoots only Zeiss glass. I have shot with him multiple times using both Nikon and Canon glass. My photographs are better than his because he sucks as a photographer. What a waste of Zeiss glass. I shoot Canon because in the mid 2000s, they had better autofocus lenses than Nikon. Now I am committed to Canon because of my lens investment. However, the next lens I buy will be a Zeiss 21mm f/2.8. From a historical perspective, Canon has always excelled in long lenses. Zeiss had better contrast (t* coating) and Leitz made great wide angle lenses. Their long lenses were lacking. At least compared to Canon. The reality is that skill and timing are often the most important deciders. I honestly believe that once in a lifetime photos depend on what you have at the time the event occurs. I shoot Canon because I had to make a choice. Since when I committed they had better af lenses. If I do not need af (21mm for example) I will buy Zeiss. I cannot afford Leica so that is not an option. Now I wish I was better at Photoshop, but I get better every time I use it and there you go...
Factually, Ziess' T* coating is a multicoating, similar to Canon's older SuperSpectra Multicoating. Today, Canon also has SWC, or SubWavelength Coating, which is a nanocoating...and vastly superior to any multicoating. In that respect, modern Canon lenses released over the last few years, the vast majority of which use SWC on the most critical inner elements) have considerably superior microcontrast relative to Zeiss, who has yet to introduce ANY lenses that use a nanocoating. Nikon also has lenses with better microcontrast than Zeiss, as they too use nanocoating on internal lens elements.
TDP also has some reviews of Zeiss lenses. In every comparison, flare and loss of contrast is much worse on all the Zeiss lenses when compared to Canon lenses. Hell, even my older EF 16-35mm f/2.8 L II lens has VASTLY superior flare control compared to the relative Zeiss EF mount lenses. So, sorry...but T* is NOT a Zeiss strength these days...it's holding them back.
A few years back, maybe 2005-2006 era, I'd have said Zeiss made better lenses. From a lens construction standpoint, they DO make very solid lenses that can really take a beating...but they tend to be considerably heavier than any Canon lens. Today, I believe Canon, thanks to a variety of advanced materials and technologies, makes a better DSLR photographic lens than Zeiss. Nanocoating definitely improves their lens' transmission and microcontrast, fluorite elements improve their wide-open lens performance (requiring fewer elements, which is always better than more) and help to greatly reduce weight, titanium and magnesium alloy lens barrels which are both very strong and very light weight. One cannot forget the technological improvements as well. Canon's newer lenses include advanced IS and AF technologies paired with high speed firmware, allowing them to operate very responsively when paired with a new Canon body.