When I first got into triathlons, I began to swim more and more. At first I used a traditional rubber swim cap to hold my hair back in the pool. However, it was really difficult to get on and off, and I generally lost a handful of hair in the process.
I decided to try a lycra swim cap, and bought a Tyr. It is extremely comfortable and very easy to get on and off. It never pulls my hair. Unlike the rubber swim caps, when I remove it, it does not leave a large mark around my face. So, it is tight enough without being uncomfortable.
It is not waterproof, so if you are looking for something to keep your hair from getting wet, this is not for you. I found that using a rubber swim cap left most of my hair wet anyway, so I opted for the comfort of lycra over the waterproofness of the rubber.