As far as which RDA to buy, a lot of the performance of it will be based on how well you build your coil. The trident seems like it is nearer to the original, but I have not used either.
I don't particularly care for drippers, but the Immortalizer clone on Fasttech did catch my eye the other day and I ordered it. The clone has a ceramic base similar to the original. At the very least, it should not heat up as much as a standard dripper.
You don't have to buy a mech to use an RDA. I would recommend a regulated device, like a Vamo, Zmax, MVP 2, etc... It will tell you the resistance of your atomizer once you build it. The regulated devices also have safety features that will protect you from a battery exploding in your face. If you are planning on building coils that are super low resistance (like under 1.3 ohms), you should wait until you have a good understanding of rebuilding.