What's the difference between modular and semi-modular?
A modular synthesizer has individual circuits held as modules that have to be physically connected with patch cables in order to route control signals and audio between them. A semi-modular synthesizer has the most common connections already patched for you behind a singular front panel while allowing you to bypass and repatch those connections via sockets on the front.
What's the best modular synth for beginners?
Of all the marvellous synthesizers in our round-up I would recommend the Moog Mother-32, which you can buy separately from the Sound Studio bundle; it would be the perfect synthesizer for someone wanted to get started with modular synthesis.
Which synth has the best sounds?
That all depends on what sorts of sounds you like. Many synthesizers contain similar sound generating circuits and so can have very the same sort of synthy sound. But really the sound comes down to what you are going to do with these simplest of waveforms. Are you going to be creative or are you going to keep them unadorned and pure? You shouldn’t be looking for the best sounds in a synth, you should be looking at how to improve your creative approach to crafting the best sounds from whatever synthesizer you are using.