For me, throwing Westside only was a really easy transition for me because many of my primary discs are Westside discs anyways. For long distance back hand throw I throw the King or Destiny, the world for Forehand distance. The Stag is one of my favorite control drivers and I use the Hatchet all the time for understable shots that need to go straight or turn right. The tursuas is the disc I use when I need understable, and the Warship was a staple in my bag until I lost it. Westside putters aren't all that bad either and I like the feel of the Shield for putting. The Swan makes a great straight throw approach/short drive shot and the Harp is excellent as an overstable driving putter.
When throwing only Westside, the only thing I really missed and felt that wasn't adequately available is my precious Lucid Justice. I just use that disc so much for utility throws and approaches. While the Harp is somewhat similar, the harp I'm using for testing purposes is in medium blend and I can't forehand consistently with soft plastics.If I had to throw only Westside, I would probably also get a VIP harp and could adequately use it to fill that role.
The other disc that initially I was really missing is my Discraft Flick. The Longbowman is fairly similar, but took some getting used too as it glides more and is not quite as overstable. Over time I could definitely live without the Flick if I had to.
All in all, if I could only throw one brand of discs, Westside would be at the top of my list.