Ros identifies Guil as the dominant personality. Ros is very open about his reliance on Guil. When Guil yells at him for being unoriginal, he says, "I can't think of anything original. I'm only good in support" (3.105). He often lets Guil bully him and walk all over him, and, bizarrely, he doesn't even distinguish between himself and Guil. He responds to both names.
Stoppard once described Ros and Guil as "two halves of the same personality." What we find interesting here is how two people, when they spend a ton of time together, can become dependent on each other, each filling certain roles for the other and vice versa. The bit about Ros answering to both his and Guil's name is a somewhat hyperbolic – that is, it's exaggerated for comic effect. But we think that the main message is that when two people spend as much time together as Ros and Guil do, they really do become indistinct.
But again, things are a bit more complicated than they look at first sight. Look at the scenes with Hamlet and Claudius again. In the context of Shakespeare's Hamlet, Ros comes across as the more dominant of the two. Guil often goes silent and leaves Ros to do the talking. Of the inactive pair, Ros is actually the one who is more active, even if he's not the leader. It's only when it is just the two of them that they fall into their odd roles, with Guil bullying Ros and Ros submitting to it.
From the very start of the play, Ros is established as the more sympathetic of the Ros-Guil pair. In the stage directions, Stoppard writes, "ROS betrays no surprise at all – he feels none. However, he is nice enough to feel a little embarrassed at taking so much money off his friend" (1.1). Ros is nice. He's more likable than Guil.
Later, Ros asks Guil which hand he is holding a coin in. Guil realizes that Ros had coins in both hands, and he can't understand why he would do this. Ros's answer is simple and straightforward: "I wanted to make you happy" (3.87). Happiness is a virtue Ros holds that Guil does not. When Guil's spirit is broken after the pirates have attacked their ship, Ros tells him, "Be happy – if you're not even happy what's so good about surviving" (3.313)? It's a perfectly common sense view, but it's something that Guil misses. Ros is much more tuned in to how he treats the people around him and whether or not he is enjoying himself. He's got people skills – a type of intelligence that Guil might be seen to lack.
In many ways, Ros is like a child. While Guil constantly seems weighed down by existential angst, Ros is able to have fun. He is more excited by the Tragedians. Even at the end of the play, when it is revealed that the Player has faked his own death, Ros still feels the need to applaud and cheer him on. He also becomes giddy while they play "questions," and, as with the coins, he beats Guil at the game. Ros seems better at getting enjoyment out of life than Guil does, and his view of a play is not one that will mirror reality, but "a good story, with a beginning, middle and end" (2.322). He likes to be entertained.
A last point, but an important one: when the pair finds out that they are taking Hamlet to his death, Ros points out, "We're his friends" (3.200). He ultimately submits to Guil, but it is clear that he cares. He understands personal loyalty and, if he were not so servile, these might be the virtues that he lives by.
Ros is smarter than he thinks he is. He's prone to misunderstanding Guil and the Player, but, in his defense, the two aren't always all that clear. When the Player tells Ros and Guil about how Polonius thinks that Hamlet is in love with Ophelia, Ros thinks that he means that Polonius is in love with his own daughter. He exclaims, "Good God! We're out of our depth here" (2.193). He often concludes prematurely that he's in over his head and he doesn't know what's going on. But, when you get down to it, he's actually pretty clever.
This becomes more apparent as the play goes on. His most prolonged monologue is on the subject of death, and is much more silly than Guil's is. Yet, there are flashes of brilliance. At one point he says,
We must be born with an intuition of mortality. Before we know the words for it, before we know that there are words, out we come, bloodied and squalling with the knowledge that for all the compasses in the world, there's only one direction, and time is its only measure. (2.227).
How cool is that? Admittedly, though, if we just saw these lines and hadn't read the play in awhile, we'd guess that Guil was the one who said them. But Ros is also capable of some philosophizing.
There's something different about the way Ros philosophizes though. The engine that drives all of his speculation is common sense. He doesn't go off talking about death as the "ultimate negative" or something like that: he talks about how it would feel to be inside of a box. He's a very practical-minded guy, so his speculation is very grounded. When Guil wastes his time trying to determine the direction of the wind based on the position of the sun, Ros suggests, "Why don't you go and have a look?" (2.50). Guil gets angry with him, but it makes perfect sense. Ros is a pragmatist.
In interviews, Stoppard has commented on how his characters can be indistinguishable, and that it's often possible for one character to say a line that could just as easily have been given to another character. Consider Ros's, "We drift down time, clutching at straws. But what good's a brick to a drowning man?" (3.169). As we've noted, this sounds like something Guil would say. It makes each character many-layered. One can't simply label Guil as the smart one and Ros as the knucklehead. The two are distinct, but they share many qualities as well.