hmmm maybe I should get Omega just for Flare...
And Lash both of the abilities are good.
I would say Lash is the better just because Flare is much more situational based on it's super long recharge time that definitely has to be worked around. Infiltrators can ignore the cooldown altogether with Tactical Cloak (assuming you like to add biotics to non-biotic Shepards). As for Adepts using it with Warp (well anyone I guess since Liara learns Warp) it will kill Centurians, Marauders, Ravagers, Cerberus Shield Pylon clusters even if Shepard focuses on Recharge Speed (lowering it's cooldown to ~4.5 sec) it's still a long time and shouldn't replace the standard Prime/detonate with Throw combo for single enemies or smaller groups of basic unshielded mooks. The key is to know that it is to know when to use it and when not to. But for those larger, better defense groups it can turn using a series of combos into a one-and-done deal, allowing Shepard to move up to a new location while it recharges. I should note that it works much better with Liara, who can prime with Warp, even enemies behind cover, this will also immobilize them temporarily so they don't dodge it which makes me feel silly.
Lash is also amazing and in most cases I would say it's better. It's basically an awesome combined version of Pull and Throw. It has a quick cooldown (~ 1.1 sec with a +200% weapon loadout). It will grab enemies and hurl them into the air with the right angle, with the shield piercing evolution it will do this to shielded enemies and Kai Leng. It also both primes and detonates biotic combos with a combo damage evolution. Plus, it will strip those pesky Guardians of their shields.