If you could choose only one...

[Roadkill101]

Basic/Expert, it's the only sytem listed that I have any real familiarity with. I have a later boxed edition of the OD&D that I've read through, I find the Basic/Expert game a little better fleshed out and more to my taste. Don't know anything about the other systems.

 

[Arnwyn]

I'd go with Castles and Crusades, because it gives me the feel of D&D, but the most important conveniences of 3E.

C&C, for this reason as well.

(And, just as importantly, the support that's coming along with it.)

 

[jdrakeh]

Also, due to recently supplments with the concept of the Mythic Companion, it is possible to expand the world so it is less magocentric and quite heroic.

I have an extreme interest in using Ars Magica as my all around fantasy system, so this concept appeals to me - which supplement covers it in the most depth?

 

[Mercule]

I don't know enough about three of those choices to make a truly informed decision.

However, of the two remaining, I think I would choose D&D (Basic/Expert) based on the way it pushed out certain classes.

Ditto. I'd love to try all of them. Since the question sounds rather permanent, however, I'll go with a system I know is fun, easy, and would be accepted by my primary group of players.

 

[Kahuna Burger]

As I've never played any of them, I would choose the one with the cheapest books.

 

[drothgery]

Ars Magica's the only one I'd be even remotely interested in, though I've never played it. I just don't know anything about BRP, wouldn't be playing 3.5 all the time if I preferred pre-3.x D&D (and since C&C reintroduces so much of what I disliked in 2e, I can't imagine ever touching it; if I wanted a simpler D&D-based game, I'd play True20). The default setting for Ars Magica, and what I've read of the mechanics seem interesting, at least.

 

[Imret]

Hmmmmm. Having played none of the systems listed above - don't blame me, I got started gaming on the PFRPG - I'm going to vote Ars Magica, but only because I've read good things about it here on the boards, particularly their magic system.

 

[Dragonhelm]

I'd go with Castles and Crusades, because it gives me the feel of D&D, but the most important conveniences of 3E.

Agreed. It's also flexible enough to be house ruled to the heart's content.

 

[EdL]

As I started GMing with Runequest I voted for BRP. Of the others:

Basic/Expert D&D would be my next choice.
OD&D doesn't have enough rules to bother with.
I've never read or played either of the other two.

 

[Shadowslayer]

And finally, C&C seems to me to be a way of reintroducing all those old flaws back into 3.x -- no thank you!

I'm curious to hear what makes you say that. I've always considered C&C as old fashioned AD&D with the flaws edited out.

Anyway I chose C&C. For ease of DMing, ease of learning, and ease of houseruling.