I have been using Contax equipment since 1985. Over the years, I used 5 different bodies, a Yashica FX-7, then the Contax 139q, the 159MM, and the RTS's I & II. Today I still use the RST-II, and I'm presently debating whether I should upgrade to an RTS-III or just move to the newest N-System.
The lenses I used the most are (and were) the 25/2.8, 35/2,8, 50/1.4 and 100/2.0. I especially remember an expedition in Northern Saskatchewan's forest (Canada) in 1990, when I carried both an RTS-I and a 159MM; the best pictures I took were all made with the 25/2.8, a gem of a lens in my opinion, with natural perspective and fabulous color rendition. I made amazing pictures of waterfalls in the northern forest with that lens. I parted with that lens a few years ago because I was in desperate need of cash, and today, I wish I didn't! Nowadays, I mostly use the 35/2.8 and the 18/4, since I mostly do urban landscapes.
A few days ago, I have acquired a 85/2.8 from eBay, but cannot comment about it just yet (too recent); however it is much more lightweight than the beautifull 100/2.0, so it's possible I will start carrying this lens with me on my nature treks next summer. The 100/2.0 is a fabulous lens for sure but it is big and heavy. Practicality is also a consideration.
In the end, the lens you use most is the lens best suited to your needs. It depends on a variety of factors. If you're doing mostly fieldwork, you'll prefer those slower but much lighter lenses (25/2.8, 35/2.8, 100/3.5, etc). If doing a lot of studio pictures, marriage or portraits, than you will probably benefit from using those faster lenses (28/2.0, 35/1.4, 85/1.4, 100/2.0, etc.)