What if? You are in charge of programming the Omnitrix.

So choose ten different extraterrestrials beings across the galaxies and universes aka the fictional worlds like Marvel,DC,Metroid & etc are allowed for the heroic brown haired guy at protecting the earth from many dangerous threats.

Bonus event. Ben with the new Omnitrix from you and has master control & Ultimate evolution setting as well is sent to your favorite universe since the Beginning of the series as an extra ally.

 

1. Sabgheili aka Elite. Halo. Clocking in at an average of 7'4" tall and weighing in at 310 lbs of pure muscle, the Elites of Halo are no joke. Physical powerhouses and thanks to Omnitrix BS covered in armor! Great for up single target close combat and making wart wart noises. Comes equipped with a fancy plasma sword.
2. Cybertronian aka Transformer. Transformers. Giant. Fucking. Robot. Nuff said. Great for fighting larger threats.
3. Avatar aka Warp. X-Com 2. Teleportation, Mind Control, Psyonic storms, the avatar from X-Com 2 does it all and doesn't sacrifice physical strength or speed. Fantastic for multiple target close combat or quick escapes.
4. T. Yoshisaur Munchakoopas aka Yoshi. Mario. Ok hear me out on this one, Yoshi is stupidly fast, insanely durable, and monstrously strong. There are multiple respect threads dedicated to this green dino. But Jimmy, he's not a an alien. Then explain to me how you find Yoshi eggs in Mario Galaxy 2 you nerds? Great for land travel and enemy containment.
5. Thanagarian aka Hawk. DC Comics. Take a person. Now stick wings on it. Then add Nth Metal to the body, give it hawk like vision, and enhanced hearing for good measure. The Thanagarian doesn't look that impressive when compared to many other aliens, but you'll have a damned hard time coming up with a better species for flight based combat or tracking in general.
6. Irken aka Gizmo. Invader Zim. A species that specializes in creating the most complicated of doomsday weapons and conquering worlds, the Irken would be the go to for any tech work that our young hero has to do. Be careful though, too long in this form will bring out the Control Brain's programming of world conquering.

I can't actually come up with any more aliens that don't become redundant with the ones I've already listed. Maybe something for underwater or space combat? Don't know.

 

That's cool choices

 

Necroing,cause looking for Ben 10 Stuff and found this

1 Krytonians cause power sets (DC)

2 Saiyans cause power sets(Dragon Ball)

3 Namekians power set and has Regen (Dragon Ball)

4 Martians cause power sets from (DC)

5 Czarnian(Lobo'sRace) cause power sets from DC

6 Daxomite cause power sets and are a cousins to Krytonians (from DC)

7 Coluans(Brainiac's Race) cause power set (from DC)

8 Ditto(a Pokemon) the reason I'm picking this is simple the omnitrix collects DNA from all sentient beings meaning since Pokemon are technically sentient the omnitrix or the collectors of DNA for the omnitrix will collect them

9 Dragons from Dragon(i.e Shenron,Porunga,and any wish granting dragon) (from Dragon Ball)

10 units from Planet Cray reason they are technically all sentient meaning the omnitrix will scan and collect you can be Spider-man cause he is a Cardfight Vanguard card