Mike,
The first RLs were better than the first-gen STs, what in fit, finish, handling, tires, shocks, etc. If you are going to use the vehicle like a truck, then you are better off with an first-gen ST, get one used.
However, if you need a 5 passenger SUT (sports utility truck) that you want to hold its value, ride comfortably, have little issues with for the first 100k miles, then I would recommend the RL over the STs, even the new 2nd gen STs.
Ford has done a great job in improving relability in the new generation STs, and make them ride a whole heck of a lot better. If you do decide on an ST, steer clear of the V8, because for watever reason Ford seems to have many more tranny issues with the V8 than the V6.
Personally, given all the new generation ST tranny issues, and the high incident rate of the tranny issues on the previous generation STs, I probably would buy the RL over the ST, if buying new, again, tomorrow. Of course, if I knew I was only going to keep the vehicle for 70k miles, I might chance the ST if it was a GREAT deal.
TJR