So what do I do? Well, it all depends on the circumstances. Does this seam need to match another seam? Or do I just need to ensure the seam line is aligned?
If I'm trying to match up seams, I like to nest them, so that they oppose. Which goes which way? I work with other construction seams, and try to press away from the bulky seams where possible. I also do the little twirly thing in the middle of a four patch seam that splits the seam allowance and distributes the bulk... but that's another discussion entirely!
When it comes to triangles, I have a secondary strategy. I like to be able to see what I'm doing. That is the secret (I believe) to achieving better points.
First up, where the triangle pieces are joined together (like half square triangles), I like to press them open. Yip, open. Give it a try - it makes little difference to the ability to nest (except maybe pinwheel style blocks) and disperses that nasty lumpy seam.
Now, look what I did in this example, the triangles were pressed open, and the seam joining the two units was also pressed open. I knew that this join did not need to be matched up with anything, so wasn't worried about nesting. By pressing the seam open I get good visibility of where that triangle point is going to be, when I sew both top and bottom sides to the next pieces. If this seam did need to match - I would have pressed it one way... either way, nested the seam, and hoped for the best with the alignment. Knowing that my 1/4" seam is pretty consistent gives a certain amount of confidence.
When I joined the unit to the solid square, I could easily see where the stitching line went, and then reverting to the original philosophy, knowing that this section did require matching with the adjoining unit, I pressed away from the bulky seams, so towards the plain square - ready to nest with the next seam.
By pressing towards the little square on that side unit - I could press away from the bulky seam, and also allow the two units to nest. Love it when that happens. Once that unit was attached, I have the option of pressing it to the left - which would give good visibility for the top triangle, but hides the intersection for the bottom triangle...
And vice-versa if I press it to the right...
The solution in this case is to press this seam open, which gives the best visibility on both the top and bottom triangles. Plus, this seam does not need to match with its adjoining units - so I don't need to worry about nesting.
How do you tackle your seam allowances?