Personally, I consider there to be two different classes of portable headphones: commuter and adventurer.
Then there are 'transportable' headphones. These are headphones you can easily store away to take with you to a hotel room or something but ultimately don't lend themselves to use while on the go. I'd classify the Spirit Classic in this category, as it has a ridiculous 300 foot long cord (okay, a slight exaggeration) and the finish doesn't look that resistant to abuse.
As for portable stuff...
Commuter 'phones are those I'm comfortable wearing on the way to work and don't mind use around campus, stuff that's comfortable while out 'n' about but in low impact contexts. The M50 and Paradox push the limits of this, bordering on 'transportable,' but they still work pretty well in these roles for me. Even though the Spirit Professional is smaller and lighter than both the M50 and Paradox, I'd include it in this category for a different reason: because it doesn't seem that rugged.
By contrast adventurer 'phones are those I wouldn't mind wearing while exploring the city, going on long walks through treacherous terrain, or fighting sword wielding skeletons. They have to be rugged, able to withstand abuse AND lightweight, small, easy to tote around. The Amperior would be in this category. Maybe the Sony 1R as well.
