Hey Denny

I guess I have posted pretty frequently about tungstens over the years.

To speak specifically to your post. 

I have no real prefrence in electrodes for manual DCEN GTAW of materials of any thickness. I view Thorium, Cerium and all the flavors of Lanthanum to be pretty much equal. 

For Semiautomatic GTAW (with AVC adaptive feedback control) our trials proved that Lanthanum 1.5 (bavarian alloys) was the most consistant. This was important because we had schedules that called for 300+ arc strikes and arc on times that could run as long as 9 hours. Other electrodes (even some with the same class by different vendors) would tend to accumulate dust at the tip from the emitters that are produced during arc on time, this dust would have a negative effect on arc voltage control and cause an inconsistant arc with less favorable bead profiles.

For DCEN and AC combined use  I prefer Cerium (orange)  Very versatile and if the cerium overheats it tends to round at the tip rather than forming nodules or spitting/splitting.  Lanthanum  tends to have a rougher end when overheated on AC and more arc wandering at lower amperages than with cerium.

For AC specific applications I prefer Zirconium for lower amp fillets because it will keep an arc at the tip a bit better <I find this especially true with inverters with variable frequency>.  Cerium is next in my opinion.  Don't waste money on Pure (green) electrodes.

The cost difference between Thorium, Cerium, Zirconium and Lanthanum are really just a few bucks per box so I don't see price as a limiting factor.

In the entry level training atmosphere it is tough to keep the learners from sharpening both ends of the electrode and making identification impossible. Still we use a variety of different electrodes so the students can see what happens when each is overheated.

So in the end many choices can be good... And it is also good to keep in mind that Tungsten Electrodes are produced by the Powder Mettalurgy process and different manufacturers are going to make electrodes of the same AWS conformance catigories that may have very different hardness, fracture and extended arc on qualities. This is especially evident in electrodes 0.040 and less in diameter.

But for the average Joe, it makes little difference which electrode is chosen for DCEN, Thorium, Cerium, Lanthanum (family) or the mixes. As long as they comply with procedures. Plain Carbon, Stainless, Ti, Waspalloy, whatever... For most manual operations between 15 and 100 amps they are indistinguishable.