There really isn't much of anything positive that readers can say about Tom Walker. Two of the first things that always come to my mind about Tom are that he is stingy and spiteful. He makes conscious decisions to not share anything with his wife, and he actively avoids spending money on basically everything. He's cheap, but based on his attitude about his wife, I think that he's intentionally not spending money on his own home just to spite his wife and make sure that she is just as miserable as he is.
Her husband was continually prying about to detect her secret hoards, and many and fierce were the conflicts that took place about what ought to have been common property. They lived in a forlorn-looking house that stood alone and had an air of starvation. A few straggling savin trees, emblems of sterility, grew near it; no smoke ever curled from its chimney; no traveler stopped at its door.
One of my favorite parts of the story occurs when Tom tells his wife about the Devil's offer. Mrs. Walker urges him to go for it, and he is genuinely tempted; however, he flatly refuses just to be contradictory to his wife.
However Tom might have felt disposed to sell himself to the devil, he was determined not to do so to oblige his wife; so he flatly refused, out of the mere spirit of contradiction.
The above quote does show that Tom is also greedy. He definitely wants what the Devil is offering, and Tom even decides to charge more than the Devil recommends. Despite Tom's desire for more wealth, he is ultimately too lazy to do anything about it.
If you have to say something positive about Tom, I think it is defensible to say that Tom is determined. He's determined to make sure his wife doesn't get more than him. By the end of the story, Tom also shows great determination in trying to avoid his eventual fate with the Devil. He becomes a "violent church-goer" and is always seen carrying a Bible and praying loudly.