JRDM - welcome to the site!
For extended drain intervals (the REAL reason to go with synthetics in my opinion), you can't hardly beat the ones mentioned. Of the several brands (Amsoil, Mobil, Shell and Schaeffers), I'd have to say the RTS is possibly a "best buy" to coin the Consumer Reports phrase, because it typically turns in very good wear results and usually can be found at Wally World for a moderate price. On a performance/dollar ratio, it's flat hard to beat. The others are probably a bit on the higher end of development, but in no way is that meant to be a slight on the RTS. I personally use RTS, but I only drive around 10k miles a year in my truck (Dmax/Allison), and so I typically O/FCI once, and use UOA's as verificaiton. If I drove a lot more miles per year, I'd strongly consider a higher end product, and most likely use bypass filtration too.
I would suggest you analyze what your driving patterns are going to be. Weigh your typical mileage per year against the cost of the oil changes, including the full flow filter options as well. Let the math and UOA's guide your conscience, not rhetoric.
The upside to a Dmax is that they seem to be very easy on oil; they don't shear it much and they don't seem to contaminate much. In this regard, nearly any oil will perform well in a Dmax.
Some of the core concepts many of us here at BITOG try to educate newcomers on are oil analysis and "synthetics". These are probably two of the most mis-understood and often nearly mythical topics in the world of lubricants. I, for one, have learned a great deal from contributors here like Johnny, Bruce381, Pablo, Gary Allan, The Critic, and many others. WE DON'T ALL AGREE ALL THE TIME, TO SAY THE LEAST.
But if you take away one thing from this site, please try to help educate others with thought provoking facts, rather than lore and "they say that ..." generalizations. I think it's good when we all share experiences and facts. But be careful to seperate opinions from facts. There's nothing wrong with opinions, but they sometimes take on a "herd" mentality, and grow in strength without merit.
Rather than my rambling on here about "synthetics", use the search funciton on this site (it actually works, contrary to the actions of some members) and spend time studying the UOA diesel section and this section. You'll learn a lot.
However, if you want a "Synthetic Oil for Dummies" quick answer to your post, I'll say only this:(Caution! the following is my opinion!)
There are plenty of good brands of oil out there, in many variations of weight, price, and performance enhancing attributes. If you can get out of the "gotta change oil at X,xxx miles" mentality, then UOA's and synthetics will pay you back in spades. If not, then a conventional group II oil will do a wonderful job for short OCI's, and there are millions of vehicles in service right now as proof. Synthetic lubricants and UOA's and Bypass Filtration are tools; if you don't use them correctly, they are a waste. But if you can, you will reap the benefits for years to come.
you've officially entered the world of lubricant insanity.