The best top-tier tanks are the most specialized ones: BFT Carrier and Ghost Sniper. The Sniper can turn invincible at any time, a hilariously overpowered secondary, as well as a shot that passes through enemies *and* damages any nearby ones. The Carrier just has so much firepower that nothing can blow it up.
And the least specialized top-tier tanks are the worst, especially for the final boss. The Drone Master has an underpowered special and a primary that you can't even aim; it's probably the worst tank. The Leecher Tank has a lifestealing primary, which is nice, but its special takes too long to work, especially for the final boss.
Something like 500 clicks on the last level, but I still feel good because that's probably the only sliding puzzle I've ever done without a walkthrough.
 "Demons Took My Daughter"){kind=icon}
 "Strand"){kind=icon}
 "Dude and Zombies"){kind=icon}
 "Bubble Tanks 2"){kind=icon}
 "Fracuum"){kind=icon}
 "I Wanna Win!"){kind=icon}
 "Bubbles 2"){kind=icon}