In my opinion, the FX in the HD are great. I can get them to sound pretty much just like my analog pedals. I have yet to find the perfect amp in the HD. My favorites are the Elektrik and the Plexi. I'm not saying they aren't great amps, they are just not my flavor. I want a hot-rodded Marshall sound and there is not one in the HD. My preference would be a Bogner Ecstasy with blue and red channels. Line 6 has been slow in adding new amps and although they added the much wanted plexis they did not add the amps that everyone is asking for (IMHO).
Anyway, I use the HD for practicing but for jamming with people and a live band I like my pedalboard. The main reason is because setting the HD up for different configuration is a PITA. Do you use pre amp or full amp? Cab or no cab? Mic or no mic? What output mode to use? What am I going to be plugging into?
With my pedalboard I just need to plug into any clean amp and I can get my sound. I have a Bogner Red pedal and it sounds awesome.... It's MY TONE.
I may start using the POD HD for post Fx in the amp loop (reverb, delay, pitch shifting, chorus, noise gate). But I have pedals to do this too. I like being able to turn knobs on the fly.
The situation I think about comes from a conversation I read with EVH. He basically said that since each room is so different you have to be able to adjust things on the fly in order to get your sound in that room. If you have several presets in the HD then if you adjust the treble and bass in one amp you are probably going to have to do it for every preset. If I just use the HD with some different delay settings for presets, then I still have control over my main tone on the amp and the dirt pedal.
Everyone is different, this is just what works for me. And..... next week I may change.