I went with Jeld Wen Aluminum Clad window. Very happy with them. I used an assortment of operable windows; double hung, awning, sliding and casement windows were installed. As I was designing, I tried to think how I wanted each window to open at each position and went from there. The main living room has double hung, kitchen has casement, bath has an obscured glass awning, and the loft has 2 wide sliders and a small awing. All of the window are tempered glass, which are preferable for a tiny house.
The window flashing method I used can be viewed on the TIny Nest youtube station so I won't get into the specifics about that.
https://www.youtube.com/watch?v=qsZ6xRovKVg
I did run into a problem with one of my windows. I probably wouldn't have done anything, but a friend came to my sight just after I install the two windows in the photo below and the first thing he says is, "I guess you really don't know how to install windows. They're out of square." Since the two windows stacked on each other, you could see the alignment was slightly off. I actually thought the same thing myself when I first looked at them but thought I was close enough. I ended up taking the window out and discovered it was out 3/8" of a inch, which is noticeable on a small window. I felt ecstatic that my framing wasn't out.
I installed metal flashing above and below my windows. Since Home Depot didn't carry the z-bar flashing dimensions that I needed for my exterior finish, Sal at Homestead Sheet Metal (http://www.homesteadsheetmetal.com/) hooked me up with the custom z-bar I needed. I needed 7/8" deep z-bar for above my windows to accommodate the 1 by cedar trim I was using. I used 3/8" and 5/8 deep z-bar under my window depending upon how the cedar bevel siding dove into the window trim. This flashing diverts water back outside the house and prevents it from getting behind the siding and creating wood damage.