Well I am no pro either:
a) 6011 is my hardest rod for my limited skillset to run but it is a must have for me to have around ole junky, rusty, dirty, farm equipment repairs.
b) 6013 is also a must have especially if you lack a wire feeder. Works good on really thin sheet. Also works good on repairs you will be reshaping to size with handheld power tools. 6013 shapes almost as easy as virgin steel with a carbide burr tool.
c) 7014 I like this one too. So easy to run that it almost welds itself (there is a reason it is called idiot rod and it is because it is so easy to use).
6011, 6013, and 7014 do NOT require rod oven storage either so no added expense for having them readily on hand. Any of the 3 burn equally well on AC or DC. 7014 might even burn slightly better on AC compared to DC (might be only rod you can say this for).
Do Not get me wrong 7018 (and 7018AC) have their place too, but both of these they can be quite tempermental to run on lower end welding power sources, cost you money to store the rods properly even if you have a top of the line welding power source (i.e. keeping a rod oven at temp , 24 hours a day, 365 days a year cost some dollars for electricity any way you slice it). Certainly necessary is some cases, but most of this hassle is simply not needed for almost all my repair based projects. Yah Yah I already know that many run 7018 just fine without oven storage, but those same people also readily admit they run much better from the oven in comparison and few of those people are using an AC buzzbox type welder either.