That is an opinion question and can't be answered.
ben has 1,000,900 aliens in his omnitrix
above 50 aliens are in ben ten's watch about 64
63 aliens.
You can't ,but maybe they will have a new omnitrix in 2018 that has all the aliens that Ben 10 unlocked and used
10
10
52
ben got his aliens from his watch
about 1 million. but ben does not turn into more than 50 aliens.
The Omnitrix (the watch-like device he uses to transform into an alien) has 10 aliens at time. But it happened that Ben managed to "unlock" more aliens by collecting their DNA.
10 aliens.