The answer lies above us...

As someone with a passion for astronomy, I love to read and write science fiction, featuring correct science and (hopefully) a nice plot. 

Let me give you an example.
Someone asks you to fly over to M31 (the Andromeda Galaxy). How do you do it?
Light speed may sound like a great idea at first, since anything travelling at 299,792,458m/s does not, in fact, experience time. You would be there in an infinitely small timespace, but... Two million years would pass for everyone else. And there's the matter of how to reach that speed anyway, because...
Because Einstein.
So we move onwards to our next approach. Nukes. EM drives. Solar sails. Anything which could accelerate you to a decent percentage of c without reaching it. It would take periods of time much greater than a human lifetime just to reach such a speed, but you'd probably get there in the end with a generation ship (assuming you'd be happy to leave everyone on earth to die due to the sad effects of time dilation). At least it's better than lightspeed. It's actually possible.
But maybe a little dreary?
Let's spice things up a bit. Let's move without actually moving at all; moving spacetime itself around us in such a way that we transit vast distances without ever having accelerated. So there's no time dilation. And you get there quickly. And it's just fun. But we need to find something called exotic matter, and there's no evidence so far pointing to its existence.
But it's still more realistic a concept than light speed!
Therefore, realism makes the best stories.
Thanks for reading!
:-)

You may also have seen how infrequently I upload stories... I have plenty of drafts (6), but they rarely seem good enough to upload. I'm also often busy and have little time for writing... I'll try to upload something though. I promise!