Sorry about before, I was under the interpretation you had a 430 ex ii. I just really don't like the 270 ex ii, and the 90ex on a dslr confuses me.
I really strongly advise against either still, I'd really recomend a 430 ex,as you "first foot in" of even a Nissin which are nice.
But for the two you're talking about, I'd say the 270 for the hell of it. It's honestly everything the 90 is and better, with the exception of it fitting in a tight pocket. Getting some cheap triggers will make a great side light setup.
And again, I apologize, I understand what's going on. I had to decide between the 430 ex ii and the 580 ex ii, for my first flash. I went with the 430 in case I decided off camera wasn't for me. I used some third party triggers valley twinlink, and I used them enough where I was going to buy a 580, and some pocket wizards. But, now that I've realized that lighting and studio isn't my thing, I keep the 430 as a flash for award ceremonies and events, but other wise, they Aret that important.