I've found a combination of circuitjs and a spice simulator to be quick for prototyping custom analog circuits (made mainly from discretes). Circuitjs https://www.falstad.com/circuit/circuitjs.html allows you to edit components live unlike spice simulators, but with the tradeoff of convergence issues for more complex circuits, so I use circuitjs as a playground then use LTspice as a rigorous simulator.

If it's a circuit made by composing multiple integrated circuits based on their application notes and not a custom analog design, I just use LTspice alone since you can just import the manufacturers spice behavioral model (assuming they didn't encrypt them...)