Abathur and Kerrigan synergize quite well... especially since a Kerrigan and her Aba Clone can effectively permastun a team via alternating Primal Grasp and Impaling Blades with one another... at insanely high damage... which is just enough time for Aba to get 2 rounds of both off after jumping in with a Q (Ravage) before disappearing...

Catch 2 or more opponents with the above tactic and your pretty much guaranteed the teamfight... get lucky and catch more... well it is always fun to lockdown 4 or more opponents (and watch them virtually instadie).

Nexus Blades at 20, Blade Torrent at 16, and Fury of the Swarm at 4 would all be better suited for an Abathur's Clone... at level 7 Battle Momentum might be better for an Abathur... albeit, thsoe 2 zerglings do make an impact, especially when there are 4 of them.

Level 1 really depends on who you are verse... albeit Sweeping Grasp would be best... but nothing beats that Ravage heal in terms of sustain.

Abathur Build (warning, wall of text and ramblings):
http://www.heroesfire.com/hots/guide/abathermite-wall-of-text-w-ramblings-clone-locust-strategy-5261