Panasonic HTX7 vs. Beats Solo HD

Using your criteria I'd say "Neither" 

Panasonic HTX7 are not known for their thumping bass (not without a simple mod at least). And Beats Solos are not known for their build quality (Even the HDs with their reinforced headband still feel like they'll snap because the plastic simply feels cheap as hell).

For your criteria and for the money I'd first look at Audio-Technica ATH-M50. After that, for a bit more I'd look at either Sennheiser HD25-1 II or AIAIAI TMA-1. For the latter two it depends on how you like the highs, because the HD25-1 IIs are far brighter than the TMA-1s (or the TMA-1s are far darker than the HD25-1 IIs, either way you look at it). Either way, all three sound great, and are all built like tanks. 

For the record the ES7s are also good, and are certainly better than the Solo HDs. Which btw are far better than the regular Solos, but they are still not worth the money IMO (the Solo HD vs the Solo that is), as they have more than a few problems. 

the ath m50 are probably expensive if you consider that the MSRP is higher than street price in US and you'd probably will only find them at MSRP where you are. I'd recommend the Alessando MS1.

I haven't tried the headphones you've listed, but I got the ES7 a couple of weeks ago.

I really like its sound, especially the bass (I listen to electronic music most of the time). My only complain is that it gets a bit uncomfortable after some minutes (I use glasses). The headband "mod" does improve the comfort, but if you use glasses, it may not be enough.

And if you're considering getting the ES7, try to get an amp as well. I use the iphone 3GS, and without an amp the bass is a bit weak, and the mids and highs are a bit harsh IMO. But with an amp (even the E5), the bass is much more present, and mids and highs are just right.