I started with guitar amps. Highlight was PolySix through a Roland JC-60, an amp I certainly wish I still had. I used to run synths into anything, out of fascination and necessity. I'm not a modular guy, and not an unscrew-and-look-inside electronics guy, but sound-wise, anything into anything has always been fair game. That said, it's really rare by now that I'll bother unplugging a synth from the mixer so's to try it through a pedal or an amp etc. I'm very plug-in friendly these days... and my guitars need something to do with their hands all day, so they get the pedals and amps.