I'm about as far from any expert one can get,given i'm 53 and bought my very first Rolex less than 2 years ago.
What i can tell you,is that I caught the disease pretty quick and ironically,have purchased all 3 of the exact same watches you are inquiring about,within the last month.
The sub is the most popular model,by my opinion so the reason you've seen it around so much,is because it is one of the older models and just wreaks of that classic Rolex design.
The GMT is also popular and not too much different than a Sub,again,by my opinion and the Yachmaster seems to me,not too much different than either of the other 2,except i believe the whole "Yachtmaster" name,gives an impression one must be the owner of a luxury Yacht,which is B.S. of course,but why i believe you don't see too many compared to the other 2.
My advice is,buy which ever you find most appealing and remember,they are each equal in quality and design,so either choice can't be the wrong one.
Just my 2 cents and good luck with whatever you choose!
