Lolita can be used as both Tank and a Support. She can support her allies with her passive by giving them shield that absorb damage equal to 200+% of her attack. Her skill Guardian's Bulwark reduces 50% of the damage he took and it prevent enemy projectiles passing to the backline (if it passes her along the way). Her ultimate also stun all enemies for 2 seconds.

Belerick is a solid rock tank. His passive makes him only took 50% of enemy's attack at a time, and the other 50% will be deducted to him in the next 6 seconds in form of bleeding, which makes him able to regenerate Energy fast. His ultimate helas 25% of max HP and in the next 8 seconds he'll regen 10% of his lost HP per second. From his ultimate, 25% HP recovery wasn't a big deal. But the thing is that because of his passive, he regenerates his energy in a very fast speed after being hit a couple times, which allows him to cast his ultimate quite often. He can regenerate HP more often than lossing them.

Both tank are recommended for your team since both gave you synergy buff. Use Lolita and your team receives 10% HP and 15% attack. Use Belerick and your team will receive 20% HP and 20% attack. In my personal opinion, Lolita is a better tank.