So you've already done the research on the differences between monosynths and polysynths, and you've decided a monosynth is what you're after. Now, it's time to figure out which one is right for you.
To briefly recap, a monosynth is a single-voice synthesizer that can only play one note at a time. This makes them well-suited to a variety of applications, like bass lines, leads, and soloing. Because monosynths rely on less hardware than multi-voiced polysynths, they're also often more affordable while taking up less room in your recording space. Most modular and semi-modular synths are also usually mono, though with modular systems especially, the affordability factor tends to vanish pretty quickly.
When it comes to choosing which specific monosynth is right for you, the differences are in the details. A built-in sequencer, for example, is a super useful feature to have, especially if you're planning to use your synth to build basslines. You'll want to consider other things, too, like how many oscillators the synth has, with what wave-shaping capabilities. The other super important feature is the filter, which is responsible for imparting the most character on the sound of the synth itself.
In the video above, watch Reverb's Justin DeLay showcase four affordable monosynthesizers, demonstrating what about them makes them cool and why they might be exactly what you're looking for.