I use the Easy Angle ruler for hsts, ever since I learned about it from Bonnie Hunter (before she started making her own hybrid of it). It's the most accurate way, for me. I hate taking time trimming and my hsts don't ever need a trim when made with the Easy Angle. If you want 2.5" triangles, you cut a 2.5" strip. Then you place the ruler along the strip and cut, over and over down the strip. If you use a consistent 1/4" seam, they will be perfect.
The problem for me with sewing two squares around the edges and then cutting diagonally twice, or sewing diagonally across two squares and then cutting, is that it's very hard to get hsts that are consistantly accurate. If you miss that exact diagonal by even a crumb, your hsts are off.
Here's a great video by Bonnie, explaining how to use the Easy Angle.
https://www.youtube.com/watch?v=wQ_AoJsGJbM