In my opinion, and I've been to all three, NOTHING compares to Vegas. It is the end all, be all, for me. However, Biloxi edges out Tunica for me because outside of casinos, Tunica is miles and miles of farmland (nothing else to do/see). If you need a place to stop along the way and if Tunica is a good place to stop based on timing/distance, then it's worth it to say you did it. Casinos in Tunica are spread out and navigating from one to another can be a challenge if you aren't paying attention.
If you do go to Tunica, my recommendation is Gold Strike. If you stay there, ask for a high floor with a view of the river. There are two other casinos within walking distance but all other casinos will require a drive.
For Biloxi, I recommend Palace if you don't smoke, IP if you do smoke. Scarlett Pearl is the new casino, but the slots there are tighter than a tick's tail. Beau Rivage is nice but higher table limits there.
Good luck and safe travels.
We've gone to Tunica quite a few times, but had taken a break for a couple of years and definitely saw a change in prosperity since the last time we were there. If you like cheap table games, it's definitely worth a stop because they are easy to find! We will go back....but Biloxi is now our favorite southern gambling town.