How should I use my Panasonic online discount?

ST50 or GT50 Panny plasma.

ST50 vs GT50: Go look at them to see which you prefer. The main extra you get with the GT50 over the ST50 is THX mode. IMO, the ST50 is the better value.

No, it is not safe to assume your pecking order. Many here believe plasma provides the best PQ overall. Others prefer LED. Both technologies have their pros and cons, and which is better for you depends on your viewing room situation. Plasma is generally a better value/less expensive, better viewing angles, and better handling of motion. LEDs are brighter and so may be better in rooms with bright sunshine that you can't control. Personally, I would rank them plasma > back-lit LED > edge lit LED > LCD (unless you have bright sunshine directly on your display).

The THX mode (cinema/day) don't have anything to do with audio. It is just a THX certification standard. It really makes a difference in my opinion. It is pretty close to a calibrated set and it comes with these settings out of the box. But you can't go wrong with the ST or GT. Both are outstanding.

From a personal perspective: Plasma > Back-lit LCD (CCFL OR LED) > Edge-lit LCD (CCFL OR LED)...

This should hold true within most Price/Size categories:
- the Sharp Elite is an LCD that many reviewers feel beats the majority of plasma sets for overall PQ - but also costs more than any other consumer plasma, to the best of my knowledge;
- one of the higher end Sony LCDs may well beat an El Cheapo Plasma panel - but, again, at a much higher price point;
- Personal Tastes and Specific Viewing Conditions / Usage might dictate one technology over the other.

If you like Cnet's reviews, their Top 5 2012 Panels - on the basis of OVERALL PQ (Price be Da***d) - are: Pan VT50; Sharp Elite; Pan ST50; Pan GT50; Samsung E6500 - and in that order. 4 plasma panels, and one expensive LCD.

Note that they have placed the ST50 above the GT50, even though the ST lacks THX.
Also note, however, that they rank the final 3 (ST, GT, and E6500) as being VERY CLOSE in overall PQ: features, price, and/or styling could easily sway the decision.

For my $$, would take the ST50 and "invest" the saved $349 elsewhere in my system, whether in other hardware, or expanding a movie (blu-ray) library.
But, of course, these are YOUR $$s......

Earlier this year. You'll be waiting until at least April/May 2013.

With that mentality, I would just wait until 2014. Maybe even 2015...just saying!

As info, I saved $170 on my 55GT50 by NOT using my 25% employee discount with Panasonic but instead ordering the TV from Amazon. My advice is to not assume that you get the best deal from Panasonic, their prices before the 25% discount are HIGH and retailers like Amazon and Paulstv etc will often beat the discounted price.