They are sort of incomparable, being very different shows. That said, I am myself someone who grew up with TNG, who was molded by TNG and shaped by TNG, and for whom TNG is the only good Star Trek... and I like B5 better. For me, TNG is entertainment and B5 is literature. To illustrate the difference, I will point out that TNG occasionally (rarely!) deals with death, and it usually does so by minimizing and mourning it, essentially averting the topic. Entertainment does not linger over the uncomfortable. (I am painting with a broad brush here -- I'm aware TNG sometimes does. Just not a lot.) B5, by contrast, returns again and again for full episodes to the topic of the soul-rackingly difficult moral requirement to offer comfort and face the inevitable tragedy together, and the agony of the experience and the ways it changes you.

As much as I love both shows, I wouldn't really recommend B5 to someone based on a love of TNG. I think it is more natural to recommend B5 to someone based on a minimial affinity for sci fi and a liking for Lord of the Rings, which will really tell you how different the two shows are.

TNG is wonderfully idealistic. It paints a picture of rising above your vices and being professional, civilized, and decent. It teaches you to work the problem, to examine the data, to think and consult and reflect and do better. I think it unrealistic -- I thought it unrealistic when I first encountered it -- but that doesn't matter. It's such a worthy ideal that it is worth encountering and remembering over and over again. As you go through life, you should remember that that is an option and strive for it.

B5 is wonderfully heroic. It is about dealing with a world of moral complexity and uncertainty, about trying to do good even when it is futile, about being a hero in the face of danger and risk and doubt. About how politics makes that difficult and keeps it in check and at any rate isn't a game you can check out of because it is the game.

Both shows encounter awful authoritarianism. One examines the law and philosophy in detail and gives a stirring verbal rebuke that carries the day. One starts a rebellion without certainty that it will be right or effective, but because under the circumstances, a good man feels compelled to do so. I think these are both extremely valuable takes on the topic, and I wouldn't want to have not seen either one. But I do have to say that at the end of the day, it is the second one I think of more as I go through life. For me the greater life lesson is not in taking the time to seek deeper wisdom, worthy as that is, but in having the bravery and faith to face danger, uncertainty, and tragedy.