By today:
* best value for money is Logitech C930
* best for adult webcam biz: Logitech PTZ Pro
Don't forget for best result a model should invest into:
1) Logitech PTZ Pro
2) Laptop with at least modern i5 or better i7 processor
3) Get bright light including background lightning. try to avoid dark areas in your video feed. Remember in dark light camera need more time to catch image from video sensor and keeping 30FPS become difficult. As result quality drops down. Lightning is VERY important!
4) Stable, fast upload Internet backbone with low latency (ping time) to streaming server.
Technically that's all!
The rest is how to serve your body
Few other recommendations for models:
Useful webcam modeling tips