You can't go wrong with SPOG on just about anything and everything. From there, its fielders choice. I just consider that "seasoning" though, and not really a rub. Paprika, and brown sugar are your next go-tos for rubs, and then the spice list seems nearly endless.
It is not essential to use Koshering (Kosher) salt - it is usually used because most "kosher" salts do not contain added ingredients and the grain size is often slightly larger than table salt. Be careful though as some Kosher salts can contain anti-caking agents - so it is important to read the label on the box. Most Sea Salts do not have added ingredients either and so can be used instead. If you combine your rubs in a grinder before use then initial grain size of the salt is not important.
Table salt, sea salt and kosher salt, weight for weight, all contain pretty much the same amount of Sodium as each other - 40%. Most culinary salts have some impurities (which is what gives them their distinctive colours and tastes) but these small amounts do not really affect the % Sodium.I use kosher salt for two reason, grain size and most importantly sodium content. Sea salts and table salts have a much higher sodium content. Worth looking into.
Dave - thanks for posting that - it illustrates the point nicely about the same volume of salts having different weights. It also shows that different brands of the same type of salt also vary in weight for a given volume..