Ocean for me! A lot of new divers around my area get certified in a spring-fed lake (brrr!), but I already had a trip planned to the Bahamas just three weeks after my classes ended, so I got a referral to do my checkout dives there. The vis was amazing and the water was warm, so I was completely comfortable. It felt just like the swimming pool I'd trained in, only with much more interesting sights than tiled walls!
I've been out to the lake where new divers train, and while it's a fun place to go diving with lots of purpose-sunk wrecks to explore, it's still a lake in the Northeast, so it's cold pretty much any time of year. I'm glad I was able to get my first full experience of diving in the ocean instead!