Definitely carbon steel for the sake of durability. I've got a RD9 and a BK9. Same length but two very different knives.
Desc:
BK9 - The handles happen to fit my hand well and the BK9-1 I own has the rough desert-tan grips. (I modified my other Beckers... see link
BF Link .) The knife is light and quick. Solid and sharp as h*** out of the box. Also, inexpensive. You should be able to get one shipped at $50.
RD9 - The thing is a chopping workhorse. I don't
know what I could do to damage this knife!! Thicker and heavier than the BK9 - I can't help but believe that it is far more durable of the two. But, again, a different knife from the BK9. Not as suited to the lighter work one could do with the BK9.
Humble and personal recommendation:
Survival - RD9... You don't have worry about it failing and costing you your life IMHO.
Utility - In general? RD9 for the same reasons ASSUMING your needs are heavy duty and not...

food prep.
Fighting - BK9. All right... I'm no "knife fighter" nor did any of my isshinryu training from years ago involving
using knives... only taking 'em away from your opponent. (Sai semi-qualify, I guess, but I digress...) Anyway... due to the lightness, the BK9 feels a lot quicker. That's not to say that Justin doesn't make light, fighting knives. He has several that have met with rave reviews, but I have experience with and am discussing only the RD9 here.
Tactical - What's that? I can't differentiate "tactical" from the above three.
Sorry, I have no experience with the others on your list.
Buy both??
Oh yeah... Justin and his wife Jen are awesome. He is very proud of his work and will do whatever it takes to "make things right." Truly a man of honor and worthy of respect.
Camillus (Becker), on the other hand, seems to have lost interest in the forums and their Collector Club has some pretty spotty reviews. The operator was helpful with me on the telephone, but you certainly won't get the level of personal service that you would find if you go thru Ranger directly or thru one of their largest distributors, like Sage Creek.
Search "Ranger" "RD9" and "Justin" on this forum and check out Ranger Knives forum on knifeforums.com. (I hope that last part is "allowed," if not, I apologize to the mod.) Justin's reputation is beyond reproach.
(edited to agree thx to Powell's catch

KNIFEforums)