I am coming from a humble Pod HD 500 straight into the Stadium XL Floor - although I have used the Helix Native software a bit as well, so I wasn't completely unfamiliar with the Helix sound and effects. I must say WOW , what an upgrade that was! The sounds are of course better - I would say the biggest improvement from the HD series are the cabs section (updated for the Helix around firmware 3.5) and the fact that you can load IRs, which is of course a standard nowadays. The amount of amps, cabs and effects is also a huge upgrade from the HD series.
What's most impressive is how Line 6 has made it a fun and engaging experience to try all the different amps and effects out. They are mostly dialed in pretty well from factory (the factory presets are also mostly great), and Focus View allows you to test completely different tones easily and fast.
The new Agoura amps are impressive - I am mostly impressed with the clean amps. It's not that the distorted amps don't sound sound great as well; they do, but it is hard to beat the Badonk for metal rhythms. The Revv and Panama models are very good as well - but it can be hard to justify the extra DSP, given that Badonk is pretty light weight.
In any case, DSP can still be tight if playing with 2-3 instruments and two Agoura amps per path, so sacrifices need to be made in those cases. Choosing the Badonk instead of one of the Agoura high gain was my logical decision, and it freed up all the DSP I had the need for and probably more.
The touch screen is huge, bright and a joy to use - especially for Focus View, parametric EQ and 10 band EQ. I still have to experiment more with it for the cab block, which seems to work really well as well.
I haven't used Showcase yet, but looking forward to using it for pre-recorded bass for my band's rehearsals. Proxy is not out yet, so I can't speak about it as of yet. I can tell that I am already on the fence about it, given that Line 6 has stated that one capture block should use as much DSP as an Agoura amp. I might be mistaken, but if I remember correctly from testing out the Quad Cortex, I think the capture models on the QC use a lot less DSP comparatively speaking. In any case, I opted for the Stadium for the modelling, not the capturing - but it can still be a great bonus.
All in all I am having a lot of fun with the unit, as well as dialling in some killer tones both with the Agoura models as well as with some of the original models. It was a very expensive purchase, but I am more than satisfied with the results so far.
On a sidenote, I know that the units have come out of the factory with a lot of bugs. Luckily, I have only encountered the disconnections from the computer software - nothing major, and nothing more. Furthermore, a lot of the bugs have been fixed in 1.2.1 - and knowing Line 6's track record, I have confidence that everything will be fixed soon, and new amp models will continue to pop up regularly, which just makes this unit an extra joy to have.