I use different watchfaces for different situations. Mostly I use Modular or Utility.
I use Modular at work because of the large complication in the middle that allows me to see my next meetings at work (which is very important in my job).
I use Utility most other times as it's simple, clear and allows me to see the weather including a description at the bottom which is great for weekends.
If I'm going somewhere fancy I'll switch to the Simple watchface with all the detail and complications removed, which is a pretty classy look.
At the gym or when working out I switch to Chronograph as I can use the stopwatch feature to time rests between sets or sprints.
I generally don't use the gimmicky ones like Solar, Motion, Astronomy or Mickey. Though they are pretty and good for showing off.
I like the Colour watchface but it's so similiar to Utility - sometimes I switch between the two depending on my mood.
Overall I think Apple did a great job with the watchfaces. I would like to see more though including some more digital ones, and some more abstract watchfaces. I have heard a lot of chatter about people wanting 3rd party complications or watchfaces, but I think the watchface is so critical to the working of the watch I think Apple need to and should keep this closed off. Personally I wouldn't really be interested in third party complications, what kind of info would you want to see in such a small format other than what Apple has already shown.
edit - FYI I voted Modular as that's what I use most of the day since I'm at work most of the day.