It depends on how many of each type you need.
If I'm making a lot (more than 6-8 of any single combination), I draw a grid on my fabric and sew them all at once.
When I'm using scraps, I make them oversized on purpose and trim down. You want your finished size + 1" if you want just a sliver to trim. I usually make them 1.25" bigger since I'm going to trim anyway I want there to be enough to trim and if I'm off, enough fabric to still be usable even if the angle isn't exactly perfect.
So, if you want a 2" finished HST, I'd start with two squares each 3.25". Draw a line down the middle on the back side of the lighter fabric, and using your 1/4" quilting foot sew along either side of the line and then cut down the middle to make two usable HST units.