I started self teaching guitar just over a year ago, and started Keyboard 3-4 weeks ago.
I've found it 56748936% easier to start off Keyboard than Guitar. When I say that, I mean getting to the level when you can knock out simple chord based stuff with a level of competency that would convince a non-player that you actually know what you're doing. I don't mean actually getting genuinely any good.
The thing about keyboard/piano is you can get to grips with Am, C, Dm, Em, F and G in about 5 minutes. Same 3 fingered shape, moved up and down. With that you can be convincing. EG, playing the chord part to Let it Be is piss easy after just 15 minutes of touching a keyboard for the first time. Whereas the same thing on guitar would take much longer. And I've gotta say making progress like that where you can play something for someone and have them recognise it helps a lot to prevent you giving up in frustration. Keeping up the motivation is probably the most important aspect of learning an instrument. When it takes you a 1-1.5 months just to be able to change from a 5th string root power chord to a 6th string root power chord without stopping for 3 minutes to carefully reposition your fingers, it's irritating.
So in my (very) limited experience keyboard is easier, in the early stages at least. Also, you can plug headphones in to practice without fear of others hearing you in the early stages of fail-ability. Even with my guitar unplugged, I find it hard to practice things that I can't already play if there's someone else in the house. That's probably just me though. Learning keyboard/piano also forces you to either a) learn to read sheet music, b) learn to play by ear, or c) both. With guitar, you can be lazy and get around doing those things - but you shouldn't. You should learn them. I know, because I didn't.
That said, obviously, getting legitimately good at either is very hard. My opinion? Do both.