Been having a blast with my two sentinels i have run so far.
Rad/Rad Sentinel - Reghulus
Lvl 50 with some incarnates
Fun, Hardy, certainly no slouch.
Archery/Ninjitsu Sentinel Zenn
Lvl 28 and climbing
This one is equally as fun and stealthy to boot. Archery, while all Lethal on most attacks, Hits fast and often, While Ninjitsu keeps him healthy, filled with Endurance and fighting non stop.
Id have more but im also leveling 11 others of Various AT's.