>>107103158
>Which one
FT1 will probably sound better, the midrange on the X20 looks fucked. If you want to EQ then stock frequency response is less important but you still have more boosting to do with the X20 which means FT1 would be better in that case as well. I'll say that X20 is probably better built, if nothing else. I haven't tried that particular model in person but most I've seen from that company seem to be well made.
>how do I learn to compare for future?
Look at the frequency response and distortion. squig.link has FR for most headphones and allows you to compare them directly. Deviation from the target is not necessarily a bad thing but an uneven frequency response and a recessed midrange are both things you don't want regardless. For THD ASR and diyaudioheaven are both good sources. Below 0.5% distortion is ideal but even up to 1% shouldn't be audible under most scenarios. For bass distortion can be higher than 1% before it becomes audible and bass distortion is not always unpleasant. What you absolutely don't want is treble distortion.