There are so many online casinos that accept bitcoin but BitStarz by far is the best one that I have come across. I mainly started using them due to their Nolimit City game offerings (they have all including the bonus feature buys) which is fantastic. I do like their UI on both mobile and laptop browsers as it looks great and it is easy to find games and sort by provider.
The free play option is great as well as it is offered on the majority of video slots to try them out. I have had a couple of big wins on the site and was a bit worried about withdrawals, thankfully it was super easy. For my first withdraw via Bitcoin I had to confirm the bitcoin address and received it within about 5 minutes. Amazing! All future withdrawals were about the same time.
I normally opt out of any bonuses on deposit because of the wager requirements. It is simply too large and I prefer to stick with playing with my money since it is often difficult to ever achieve the wager requirement. I do appreciate the free spins given out though and always try to push my luck with those.