There is no "best". A lot depends on where you are diving and how 108s fit on you and how they balance.
As Tobin points out, they aren't terribly negative when empty, so if you are diving cold water, the decision between steel and aluminum plate will be made more on where you need to PUT weight than it will be on managing total ballast. On the other hand, in warm water with minimal exposure protection, you might not even want the weight of a steel plate. You'll be starting the dive around 20 lbs negative from gas.
So material is situation-dependent. Brand is personal preference. There are several brands of plate made from good quality materials and with good workmanship. They have different small features, like the lower corner bend and ability to use the Cinch on the Halcyon, or the weight plate holes in the DSS (not relevant to doubles). Some have camband slots for single tanks and others don't; some have multiple holes for bolts on doubles and others don't.
With wings, you first have to decide the total lift you need, which needs to do two things -- float the rig with you out of it, and compensate for the buoyancy loss possible from your exposure protection. It's a hazard to buy too little lift, and a nuisance to have a wing that's too big. (Bungies don't solve that!) In addition, how the tanks balance for you can argue for one wing over another -- For example, I like the Deep Outdoors wings because they have a very large upper arc to park gas in to battle the head-heaviness of doubles, since I don't have any legs to speak of to get my Jet fins out behind me as a counterweight. (Those wings are no longer available, and I just mention them as an example.) Wings also vary in the size and material of the corrugated hose, and how rapidly the inflator will fill the wing, among other things.
There is no "best". There may be a "best for you and your diving environment," but we'd need a lot more information to be able to advise about that.
Although you didn't ask for it, I am also going to offer that, having been certified just a couple of months ago, you might do well to spend some solid time in a single tank setup and develop a really stable platform before perturbing it with doubles. If you are frustrated by short dives, the solution is better gas consumption and not double tanks.