There’s some regularity based on retirements and where they need people. If you just want to work at Fresh Pond, you can apply for both the TA and OA positions and go with whatever calls you first. OA operators can work at TA depots and vice versa. However, if you were to move up to dispatcher for instance, you can only work at depots in your division. OA dispatchers at OA depots, TA at TA.
If you want the city job and NYCERS pension, then go TA. If you go OA to TA, you will lose your seniority though.