Both shows have a big enough budget to look realistic and have high quality production values, so it's not that one show is handicapped monetarily compared to the other, instead it comes down to the writing and the execution.
Heroes tries to throw an endless stream of action at the viewer in the hope to keep them entertained. It seems to me an artefact of confidence, it's as though Heroes doesn't believe that the writing will carry the episode. The Sarah Connor Chronicles on the other hand believes in the writing, it's execution is nicely stylish and often understated, focussing on the characters. Even moments that sound like they could be cheesey are pulled off: take the episode where Sarah Connor was reading The Wizard Of Oz to a young boy, whilst John battled a Terminator; lovely stuff.
What The Sarah Connor Chronicles succeeds at is creating a world of interesting characters, about which we are constantly discovering something. It's the classic story essence of creating a situation to which a character must react, where that reaction shows us something new about the character. And consequently we come to care about the characters, or at least retain interest in them. Even the Ex-Rockstar Scottish T1000, of which I have been critical, had an episode looking after a child, which showed us something about the robot and it's intentions.
In Heroes the characters decisions seem unrealistic and rushed with an emphasis on twists and stunt plots, Sylar becoming "good" for example. Lost is a show that does twists well, because they are often bonkers, entirely unpredictable and planned in there from the start (more or less). Heroes plot twists feel like an exercise in attempted viewer retention.
From the beginning Heroes has bet everything on the big spectacular story arc, almost at the expense of everything else. And it hasn't paid off, because the story hasn't been strong enough. The Sarah Connor Chronicles on the other hand has a well known ending, or at least a possible one, and the story concentrates on the small battles along the way.
I should also mention Lena Headey
who does a really fantastic job of being Sarah Connor, I think she's great, and the show never ignores her. Heroes best character, Hiro, on the the other hand is given weak plots and sidelined for long periods. You would have thought that it would be obvious that more should be made of him.
Consequently, as a summation of all these things, I force myself to watch Heroes, and I really look forward to watching The Sarah Connor Chronicles every week, it's quality Science Fiction and I'm enjoying it immensely.