We are introduced to two of David's friends at school: Tommy Traddles and Steerforth. Which of the two do you like most? Give reasons for your answer.

This is an entirely subjective answer, of course, but I would say that Tommy Traddles is easily the more likable of the two. Although he comes across as a bit of a clumsy clodhopper, Tommy has a good heart, and that's the most important thing of all. He's a very kind young boy who lives by a good code of values. He believes that the boys of Salem House must always stick together, come what may. Tommy may receive the most punishment of any of the boys, but this doesn't make him bitter. In fact, it's a notable characteristic of his that he has a strong sense of decency and honor which he manages to maintain, even in the face of adversity.
As for Steerforth, well there's no polite way to say this, but he's a thoroughly nasty piece of work. Although he wants the whole world to think of him as an angel, he's anything but. His wealthy, privileged upbringing gives him a sense of entitlement, leading him to treat other people like dirt. Like Traddles, Steerforth makes friends with David at Salem House, but unlike Tommy, Steerforth simply uses David to gain status. Despite David's many acts of kindness toward him, it's instructive that Steerforth gives David a cramped, tiny room above a stable when he comes to visit Steerforth in London. It's impossible to be a friend with someone who's a user, someone who wants to take advantage of you for their own selfish reasons. So when it comes to friendship, Steerforth isn't fit to lace Tommy Traddles's boots.