What microphone should a podcaster start with?

A cardioid dynamic, close to your mouth, in almost every real room. Dynamics reject the untreated-room reflections and household noise that condensers faithfully record, and the cardioid null points at your keyboard. A hybrid USB/XLR dynamic is the upgrade-proof first buy: USB simplicity today, XLR into a real interface later. Add a boom arm before you add anything else — mic position is worth more than mic price.