I am not an expert by any means, but I too had a problem cutting straight. It's not the tools, it's the fact that they move as you cut. For me, even the best of rulers and templates moved until I added narrow strips of anti-slip stair tread tape to the backs of them. I cut strips about 1/4 -3/8" wide and 2 - 4" long, depending on the ruler or template. I placed them close to the edges and a couple of places in the middle, and haven't had a problem since. A roll goes a long ways and is available at hardware and big box stores. Before you replace your rulers, give this a try. You can also try strips of coarse grit sandpaper if you have any on hand
Regarding the log cabin template, I prefer the Quilt in a Day ruler. You cut the strips to the correct size, and have very little trimming. I tried the Creative Grids, and all that trimming just wasted time, while the markings were too confusing for this old grey head to follow. haha I prefer to cut accurately and sew carefully rather than trim everything to size, but that is just me, it may not work for anyone else.