Id choose Chamalien do to his interesting skill set and his lack of screen time in UA.
Ultimatrix due to being able to go ultimate if things get bad, plus its said to have other features the original omnitrix didn't have so it would be interesting to find out what they are. Its also more interesting apperance wise then the others.
I say the Kix are a bit stronger. Though both make the aliens stronger by giving them armor and new powers and abilities, the Kix gives the aliens a wider range of abilities then the basic electric based powers the Omni-enhanced aliens had.
Frankenstrike is a good underused alien in my opinion. He's a good alien for both short range and long range attacks, plus there is electromagnetism and technokinesis abilities.
Ultimate Echo Echo due to his wider range of powers and abilities.
They probably either forgot about it since he wasn't that big of a villain or they retconned it, which OV did quite often.
Its ok. Though it did take a more comedic route like the other reboots, it does explore things that the original didn't that make it interesting.
OS, but I like UAF equally as much.
UAF cause it takes the freakiness up to 11 (no pun intended) by including more aliens into the design. That and the form had more powers for Kevin to use against his enemies, which makes it interesting on what he would do during a fight.
Toepick cause besides being more interesting, he seems more useful in combat. Pesky Dust has a boring appearance in my opinion and is too OP in my opinion.
I chose the Ultimatrix cause its appearance was a nice change then just having another one that looked like a watch.
Ultimate Wildmutt. Even if Mole-Stache wasn't a ridiculous alien Id still pick him due to his enchanched abilities and new ones like sharper claws and sharp tail.
Though I voted for UA, I like both UA and the OS, which there was a mix of the two.
I was shocked by it given it was the first death of a character in a long time in this show, especially a likable character, but at least it wasn't in vain as it showed that the Forever Knights were serious about their goal and what was to come in that season.
I was also shocked that the writers for Omniverse kept him dead since they brought back to life this Joseph Chadwick, an unmemborable character who only appeared once in AF where he was assumed dead due to a cave in. Im glad they did as that would have made that moment in UA pointless.
Im not a fan of Omniverse (though I want to make it clear that there are some good things about it but not enough) but even if I was I would still say this arc was bad as though it had potential the writers shot themselves in the foot by retconning so much.
Rocks is more interesting then the Vreedle
Id say ultimate echo echo. He's much taller and stronger looking then his devolved form, has the ability to fly, and can make and control numerous sonic disk to attack enemies in multiple directions
Terraspin for me. He has long range attacks and can hover to avoid Armodrillo's earthquake attacks.
I choose Julie cause the two had better chemistry then any of the other girls.
Im just disappointed in not seeing more, and the ones in Omniverse didn't help as all but (questionably) Ultimate Gravattack were terrible in my opinion