Something I've been curious to ask for a while: What mass ratio do you like to use between your stages? There's often a hundred critical decisions for designing each rocket, but this one always seems to be the most fundamental for me when making the framework for a design.
Just for show, in the spoiler is a couple craft with a 3:1 and a 5:1 mass ratio. They both have decent specs and can get up to some serious mischief, but do so in quite different ways. You could alternatively have multiple stages firing at once to get into 2:1 territory at the cost of added complexity.... or even a 1.15:1 asparagus?
This isn't so much about raw efficiency (it's KSP, we can min/max 'till we're blue in the face). This is more about preference. What do you like?