@aron27 Wow. Ok then. How about I just refer to every alien in the series. First off, all the Original Series aliens are keepers in my book. This includes Buzzshock, Cannonbolt, Ghostfreak, Frankenstrike (aka Benvicktor), Blitzwolfer (although I'd rater prefer Benwolf), and Eyeguy. They were very well designed and each were greatly useful and capable. They were also greatly structured, designed, and well balanced. Very powerful aliens but not too powerful and because of that, the villains were able to challenge Ben. Even Dr. Animo was able to challenge Ben in the Original Series. The Original Series aliens also looked very much like actual aliens, hence why I have a problem with chronosapien234 stating that certain aliens like Stinkfly and Wildvine were redesigned in the reboot to look more human because they're supposed to look like aliens; not more human or have a more humanoid appearance. Either way, the Original Series aliens, or at least most of them, are a definite yes in my book.
As for the new aliens in Alien Force and Ultimate Alien, they're a maybe but the most major reason why I give most of them a "no" for the reboot is because most of these aliens are very or too powerful to the point where the villains either can't truly challenge Ben or can't challenge Ben enough. Therefore, aliens that had debuted in AF and UA such as Swampfire, Big Chill, Rath (who is freakin awesome and funny and one of my most favorites), and Chromastone are a maybe but for me, it's most likely a "no" in my book. Alien X is a most definite no. He is way way way too powerful and can end any conflict with just a blink from his eyes. Yes, Ben has to get pass Serena and Bellicus but once he does so, he is literally unstoppable against all of Ben's enemies. Even Vilgax. Alien X is a most definite no.
As for the new aliens in Omniverse, just no for almost all of them. Especially Gutrot and Kickin Hawk. My biggest problem with the Omniverse aliens is that they are just too cartoonish in their designs and functions and are just so stupid to use. I mean like really, a freakin chicken for an alien. Legos for an alien. A fairy for an alien. It's just so stupid to use and are too cartoonish. There are a few exceptions though. Gravattack is a maybe but unlikely. Atomix is very useful but as I stated before, he's way too powerful at the moment. He was one of the aliens that were mentioned in the Original Series though and I bet that if Ben were to get Atomix, Man of Action would have probably still been very powerful but if Man of Action were to design him, Atomix would have at least been more balanced. For now, Atomix is still, again, a no. I do like Feedback a lot though. He is one of my favorites in Omniverse. There is the issue that he is very powerful which could make things problematic in the reboot because, again, the villains need to be able to truly challenge Ben but Feedback is really cool and maybe a yes from me for the reboot.
I did look up Speedball and Mantisaur in the Ben 10 Fan Fiction Wiki and I guess they would be fine but I'm not entirely sure. As long as they are useful, capable, and powerful but not too powerful, then I guess I could say yes on putting them in the Ben 10 Reboot. Their abilities are interesting, unique, and pretty cool though. Again, as long as they are not too powerful and that the villains can challenge Ben enough while he uses these aliens, then they should be fine for the reboot. Here are the links to these aliens in the Ben 10 Fan Fiction Wiki.
Speedball's abilities:
http://ben10fanfiction.wikia.com/wiki/Speedball_(Zed_12)
http://ben10fanfiction.wikia.com/wiki/Speed_Ball_(A-Nine)
http://ben10fanfiction.wikia.com/wiki/Speedball_(Ben_10,000)
Mantisaur's abilities:
http://ben10fanfiction.wikia.com/wiki/Mantisaur_(Alien_Alliance)
http://ben10fanfiction.wikia.com/wiki/Mantisaur_(A-Nine)