I like a GOOD salty corned beef better than pastrami (I like pastrami, but I think a corned beef reuben, again, if the corned beef is good quality and salty, is ideal).
The CIA cookbook, "The Professional Chef" says a Reuben should have a slice of Swiss cheese between the bread and the dressing and also, on the other side, between the bread and the sauerkraut. I guess that way the wetness of these ingredients doesn't soak through to the bread and make it sloppy.
I made some homemade pastrami a week or two ago and it is my understanding that pastrami is just smoked corned beef. It took several weeks. I cut the first third too thick, but quickly learned to cut it very thin. I also made some chipotle mayo and it was dynamite on my rueben or whatever you would call such a sammich - A NickDanger, perhaps?