I think it'd be easier to remove him on psych, using the 25th ammendment. If they evaluate his sanity, there's no way he'd pass it.
To impeach they'd have to find a big enough crime... and you can pretty much take your pick of several dozen, but they're all ongoing cases. I'm confident he can be impeached for multiple of them, but that'll be down the road a ways due to the slow investigative process. We already have obstruction of justice -- several counts -- but it'll be better to have more than that. The Russia investigation is going slow because they want to make sure they have an airtight case before they bring anything out. It's not something to do lightly.
I'd rather ride it out and wait and take him down on provable cases, because if we take him out for just being insane, his idiot followers -- like completely worthless piece-of-shit PkrBoy here -- don't understand science and will try to cry that "our Donnie's not crazy!", even though Trump's manias are so directly out of the DSM-5 that they're practically the best examples possible. His followers will do anything to avoid having to admit they were stupid enough to elect a corrupt headcase. So even though he'll do more damage staying in office longer, I'd rather get an iron-clad criminal case against Trump, in conjunction with the psychiatric case, so his cultish supporters will have less wiggle-room to defend him. If Trump's taken out by any means, a lot of 'em are going to feel robbed of their "messiah" and get violent. And I don't mind shooting back at them and am equipped to do so, but that kind of thing should be avoided as much as possible. The stronger the case, the less civil unrest from Trump's befuddled cult of fuckwits.