I'd encourage you to learn to cut with a flat blade first. Once you're comfortable with that, then try out the spiral blade. It's easier to start with flat blades then learn spiral. However, I found if you start with spirals, it's harder to go back to learn flat blades. Once you know how to use both blades, you can choose the style that best suites the project. I like to use spiral blades for cutting portrait style projects and flat blades for everything else.
The smaller the blade, the tighter the curve, but the more squirrely it can become on thinner materials. Larger blades cut through thicker material, but harder to turn tight corners.
Here's what I use:
#3 scroll reverse - my go to blade for most things. Cuts 1/8" (stack cut for better control), 1/4", and 1/2"
#5 Scroll Reverse - 1/2" and 3/4"
#9 Scroll Reverse - for 3/4"
#3 Scroll Reverse Spiral Blade - Portraits
2/0 or Puzzle blades for puzzles.