I think that the problem with lava rocks is that too much grease builds up in all of those little holes and eventually leads to flare-ups. This can be minimized by cranking the burners up on high after cooking is finished to burn off the leftover grease, but I think that a lot of people skip this. Using ceramic briquettes instead of lava rocks can help. Lava rocks are definitely getting harder to find. I use them as filtration media for my pond because they used to be easy to find and cheap. Not so much anymore.
As far as what's available in gas grills these days, I'm not going to be much help. I have been using the same gas grill for 16 years now and it's still going strong. It's a Holland brand grill. I use it year-round and almost daily during the summer months. They are not the fanciest grills available, especially by today's standards, but they are built like a tank.
AFAIK, the idea behind flavor bars is that the grease drips down onto them and burns off almost instantly, which reduces the chance for flare-ups. My Holland grill has a large stainless steel plate above the burner, across the whole grill that kind of serves the same purpose.
I have found that the best way to cook most meats on a gas grill is low and slow with the lid closed. This is what Holland grills are known for. Their BTU rating is actually quite low compared to other grills but if you keep the lid closed everything cooks slow and in its own smoke that's created by the grease dripping down on the metal plate (same idea behind the flavor bars). If you cook with the lid up you're losing all of the flavor into the air. Holland's slogan used to be, "If you're lookin', you're not cookin'."
Porcelain-coated cast iron is much better than porcelain-coated steel. I think that stainless is a little harder to keep clean than porcelain.
Oh well, I am falling asleep at the keyboard...the rest of my 2 cents tomorrow.