I liked more when a player could have a char on a system-owning faction and another on a non system owning faction. That was when the server was not fully RP, and nSo factions were purely RP. But now that all factions must be RP, the rule became obsolete.
I've always worried about players being on both sides of a war at a time. Secrets tend to slide that way...
I think a player should be allowed to be on more than one faction, but if said factions go to war, a player will have to be obliged choose a side. It's most flexible that way, because It allows a player to make more than one single RP, and sides' numbers become less obscured that way. Take as example the last battle between the HF and SCRA. How would have that ended had tank used his SCRA chars? Or RAZR on SA instead of HF?
Currently, its a bloody mess to plan a war from the tactical point of view because you do not know if your troops are going to be on your side or the other.
Still I like more the "A player can be on ONLY one faction at a time", but the above mentioned rule is less restrictive for those players who like to follow more than a single RP line..
So:
Anarchy way:A player can be on all factions no matter what. <- It's a mess to plan an offensive/defensive action because you have no idea whether a player will be on your side or not. Faction numbers, activeness, etc are impossible to estimate.
Semi-Defined way:A player can be on more than one faction, but MUST choose sides if said factions go to war directly or indirectly. <- More ordered, but we still have many "Ghost" factions. Those are factions formed by the same people flying under different tags. And as such, those factions never go to war among each other because these are formed by all the same people.
Ordered and defined way:A player can be part of a single faction only. <- Numbers are well defined, faction activeness is well defined too. Confrontations are easier to define and tactical scenarios are easier to plan, as you know who can be present on your side. The bad side is that a player might get bored of playing the same char once and again...
I like the semi defined way. Its not as strict as the 3rd one, and not a bloody mess like the first one.
(If you find any mistake in my English, please let me know via a PM)
(Really, I speak terrible English, so please, tell me if I make mistakes. I'd like to improve it a bit )