#1
Both ernie ball and d'addario have the same brand of strings in same gauges of

.010, .013, .017, .030, .042, .052

I can't decide which one i want because i don't even know the difference between the two.

I play main metal and i generally prefer thicker strings.

How does the Med Top/Heavy bottom compare? (D'addario btw)
#2
I like the various skinnytop/hybdrid/whatever they call them sets. Pretty much all of the string companies make some sort of set of the string in that style.

Its really personal preference when it comes to brands. Try out all of them and stick with what works best for you. A set of strings isn't that expensive so just experiment every string change.

my experiences with different brands:
D'addario sound way too modern for me and rust up really fast (they do play nicely though), Ernie Balls are decent, GHS are good, Rotosound are good, Dean Markley have this sweet deep bottom end to their sound but they rust up rather fast.
#3
yeah i personally like lighter tops and heavier bottoms so you can get nice depth for low chords but can bend the higer strings for pink floyd/david gilmour kinda stuff.

i prefer D'addarios... i tried ernie balls for a while and they broke a lot. d'addarios sound nice and don't really break and if you take care of them well... they last for a good while.
#4
the skinny top/heavy bottom strings always felt like a good balance to me. i bought a box set from ernie ball, and now i use those on all my guitars. i never tried the d'addarios, but ernie ball one are the kind i use, never had a problem with those.