Monoprice 8323 (~$28): The 8323 is a rebrand of the Kicker HP541 headphone, which typically retailed at $50. It latched on as a force in the budget market. They have unusual traits which are not typically seen in low-end headphones, such as a removable cable. They are bass heavy with a roll off in the upper mids/lower treble.
Panasonic RP-HTF600 (~$30): Dsnuts raved about these headphones back in late 2011 as the musical basshead headphone on a budget. People began taking chances on the budget performer. Even ljokerl of IEM and portable fame posted a very favorable review for the HTF600.
Incipio Forte F38 (~$30): I foresee these headphones as the newcomers to the budget block. They are rebrands of the Fischer Audio FA-004 headphones. They are very light-weight and portable, but they do not fold up. They have a "fun" v-shaped frequency response. I compared them against my Brainwavz HM3, another FA-004 rebrand, and determined the other difference was a very slight headband difference and that the pads were slightly softer. The overall sound signature was essentially unchanged.
8323 > F38 > HTF600
The Monoprices win handily in this category because they both feel sturdy and come with a removable cable. The Incipio Forte F38s have a rather light-weight and nice design with plastic and metal that feels weak but reviews have suggested that they're actually rather rugged. The HTF600 has had multiple complaints about the driver needing to be popped back into place and overall just not built to last too well.
All of them are light-weight and relatively portable.
HTF600 > F38 > 8323
The HTF600 are still an exceptionally comfortable headphone in my book. They're pretty low clamping force with very comfortable pads. The pads do tend to heat up after a while, but that's relatively minor. I used to call my Panasonic HTF600s "my for-when-the-Grados-hurt-my-ears headphones."
The Incipio F38 brings an odd angular method of resizing, but also brings a low clamping force. I've used them on the go and felt that they're comfortable enough for relatively long term listening.
The Monoprice 8323 has suffered complaints about its comfort. The clamping force is higher than either of the other two budget headphones and the headband is the last comfortable in my opinion. It's not terribly uncomfortable, but certainly the least.
Sound Quality (Treble):
F38 > HTF600 > 8323
The F38s have a sparkle in the highs that I just don't get from the other two headphones. I also noticed that they seemed less sibilant than the 8323s. I felt the F38 also was able to slightly edge the other two budget headphones in overall definition and clarity in the highs.
The HTF600 has a more subdued treble that isn't as sparkly like the F38's. I felt like there was an overall veil over the lower treble and that they were far from detailed. Regardless, they were fun enough to overlook this. I feel like the music is definitely a bit grainy sounding, like someone was rounding the edges of the sound off and approximating.
The 8323 had the weakest treble of the bunch. They had more energy in the treble compared to the HTF600, which likely is why they were also more sibilant than the HTF600. I felt like they were perhaps a bit more detailed in the highs than the HTF600s, but the way it was presented didn't jive with me. They also sounded a bit grainy, but smooth.
Sound Quality (Mids):
F38 > HTF600 > 8323
I felt like, in general, the mids on the F38 were better defined than on the other two. It's less "warm" compared to the other two exceptionally warm headphones, but they're still warm due to their emphasized mid-bass. Still, I'll give the edge to the higher clarity headphones. The mids are slightly forward.
The warmth of the HTF600 is what gave it the edge over the 8323. It's a very close competition, though. The HTF600 brings very warm, forward mids, but they felt unrefined and lacking in detail. Regardless, they are enjoyable.
The 8323s also came up slightly short in terms of the mids. Like the HTF600, they were rather forward, more forward than the F38. I found them very close to the HTF600s in overall mids quality, but just barely short.
Sound Quality (Bass)
HTF600 > F38 > 8323
The HTF600 has deep and powerful bass that I can respect. Sub-bass coming from a $30 headphone is very respectable. It has a solid mid-bass hump as well. Bass is what the HTF600s are designed to do and they do it very well for the price point. I did notice that the bass felt "slow" and loose, however. If you play quick paced bass songs like Zabava, the HTF600 almost feels like it falls behind.
The Incipio Forte F38s on the other hand roll off the lower sub-bass frequencies. I found their bass overall more punchy, but with less slam compared to the more bass heavy 8323 and HTF600. I found their bass a bit more defined and tighter, but the inability to hit those lower frequencies with authority made them drop behind.
The 8323 has more bass impact than the F38s and less than the HTF600s. They definitely have a mid-bass hump, but their sub-bass is more rolled off than the F38. Once again, they're behind in terms of overall sound quality, but not by a huge margin. I actually preferred mid bass on the 8323 compared to the HTF600's, but it was not enough to raise its ranking.
Other Sound Notes:
The 8323 had the most narrow soundstage. The F38 had a surprisingly decent soundstage for a closed headphone. The HTF600's sound stage is very exceptional for its price range -- I think this is partially because it is semi-open rather than closed.
Of the three, the F38 required the most power to reach the same volume.
Overall instrument separation seemed to go F38 > HTF600 > 8323. The HTF600 edged out the 8323 partially because of the significantly larger soundstage, despite having more of a bass presence.
Isolation was significantly better on the 8323 compared to both the F38 and HTF600. Their low clamping force and the HTF600's semi-open design both hurt them in terms of outside isolation.
Aesthetically, the F38 comes in a variety of colors, which can be nice if you're looking for stylistic options.