Depending on server, its tank or healer usually.
For The Shadowlands, I would say tanks are harder to find...but not by much. My healer only take about 10-15 minutes at most for a FP queue. It's usually alitle bit faster on tank.
It's also faction specific as well. I'm also a Shadowlands resident, and I find I generally have to wait longer as a tank pub side versus as a healer imp side. My imp side healer has insta-queues for the most part and my pub tank has a wait of 0-5 minutes generally.