I think it depends on the
counterspell, some can be considered "targetted removal", some can be considered "enablers" via protecting your win conditions, but some are versatile enough to fall into both camps.
Naturally then, you want to play as many counterspells that are versatile enough to do both. This means
a.) they are cheap enough that you can still have enough mana to use them if needed when playing your win conditions and
b.) they aren't super restricted in what they can target. So my rule of thumb for these "versatile" counterspells is anything with a cmc <= 2 that can counter
at least any noncreature spell or "higher" (i.e. counter anything).
In my experience have come to consider the following counterspells as "versatile":
[[Counterspell]][[Delay]][[Arcane Denial]][[Negate]][[Swan Song]][[Force of Will]][[Dovin's Veto]][[Countersquall]][[Mana Drain]]Usually, this means you can play about 5-7 of the above spells with no issues from color or price restrictions. If you're looking at playing something closer to 10 counterspells, I'd fill the remaining slots with higher impact, "targetted removal" counterspells such as
[[Counterflux]],
[[Cryptic Command]],
[[Mystic Confluence]],
[[Dream Fracture]], etc.