Professor X is basically the X-Men version of Nick Fury, and he's just as good if not better. You only get one round with the Professor in play, but boy does he make the most of his short life. Confusing the villain is the most powerful on average of the three modes, and the Professor represents the first time we are seeing a confuse ability on a neutral card. When playing solo, I usually default to Justice since confuse effects and Under Surveillance are so important against main schemes with low thresholds. Now the other three aspects will have a card that can fill this role. Readying an X-Men character is a great fallback if the villain is steady or stalwart and makes the card never dead if you have an X-Men hero. Stunning a minion will be the least-used mode, but really clutch when relevant.
Like Nick, the Professor loves ready effects from Command Team or Get Ready because the forced discard will otherwise make him 'waste' his second point of health, assuming you are blocking with the third point. As with any busted ally, Leadership will usually be the best home thanks to Make the Call giving you essentially 4 copies, but the Professor is truly playable in any deck, and you don't even have to be an X-Men to get 90% of the value of the card. More often than not, you will need to look for a reason NOT to play this card rather than look for a reason to play it. Only the most dedicated Avengers decks or Guardian decks might not, or a stalwart villain when your hero is not an X-Men. As far as raw value is concerned, Professor X contends for one of the best neutral cards in the game.