Two things to separate here - system and setting. System is the game mechanics. Setting is the storyboard where those mechanics are applied. So if you've played CoC and liked the system, then you have played BRP - the systems are 99% the same. The setting is flexible - use one that already exists for a BRP based game, or use one that works with any game - BRP will work regardless.
I haven't used the others so I can't compare. All I can say is that I've never seen the need to go looking past a BRP related game.
As I said above, the setting can be anything you want, so if you want to build your own, BRP will not stand in the way of that. Unique characters - absolutely. There are no classes, so you can make anything you want. Say you're playing in a modern world setting. Who can your character be? Anyone. Child, firefighter, boxer, pilot, politician, doctor, male, female, Australian, French, South African, Mongolian... the rules handle anything, or are EASILY adapted to do so. Want to make a boxer who isn't a very good boxer but knows a lot about chemistry for some reason? Go for it. Heck, the rules could handle it if you wanted to play a cat.
The hardcover does have some corrections to the softcover.
See here: http://basicroleplaying.com/basic-roleplaying/brp-hardcover-2133/6/
There are a couple errata threads here:
http://basicroleplaying.com/basic-roleplaying/typos-errata-corrections-clarifications-322/
http://basicroleplaying.com/basic-roleplaying/brp-hardcover-errata-2879/
Generic - Downloads - Basic Roleplaying Central (this one has compiled errata files you can download)
Whether a more recent printing of the softcover exists with the corrections integrated, I couldn't say. I'm sure Chaosium sells a lot more CoC books than BRP, so they have more motivation to tweak and correct the rulebooks for CoC.
Well, it depends how you want to count. The current version of the BRP BGB (big gold book) only go back to about 2008. Previous versions of the BRP being published as any sort of separate pamphlet or book go back to a booklet that was a piece of Runequest 2E in 1979.
If you want to consider the entire history of BRP related games, then you have about 35 years of back material that can be used - adventures, settings, supplements, etc. - and it will require trivial to minimal conversion. This isn't like D&D that has changed drastically over the years. I could grab the first Runequest adventure (Balastor's Barracks) from 1978 and run if using the current BRP rules with no problem.
So how much material is that?
BRP (~5 editions)
The Laundry
Stormbringer (5 editions)
Elric
Call Of Cthulhu (6 editions, plus many in between editions)
Worlds Of Wonder
Superworld
Ringworld
Elfquest (2 editions)
Nephilim
Other Suns
Pendragon (~5 editions)
Prince Valiant
Runequest (6 editions)
Privateers And Gentlemen
Mythworld
Worlds Beyond
GORE
Open Quest
Age Of Shadow
Legend
Wraith Recon
Age Of Treason
Clockwork & Chivalry (2 editions)
Renaissance Deluxe
...and I've probably forgotten something
Plus all their supplements, related setting material, years of magazine articles, and many online resources for both the above and BRP adaptations (BRP Star Wars, say). That's a ton of stuff!
Some of those are less connected to main BRP than others, but they all have enough BRP at their cores that you could mine for source material and not have to do much work on the system conversion.