This belongs in TV/Movie forum.
Star Trek vs. Star Wars...meh...How come nobody ever tries to have the Rebel Alliance fight the Federation? Oh, that's right, that's because the Death Star, and Star Destroyers are cooler.
There was an episode where a Defiant class ship (crewed by non-super human people ie: not members of the regular cast) went after pretty huge ship although maybe not a mile long and it was destroyed. There was another episode (although this happened in an alternate universe) where the (alternative universe) Defiant by flying around really fast was able to beat up a mile-long alternative version of a Klingon attack cruiser.
In Enterprise the baddies (who were ultimately defeated but were helped by people from the future) had a weapon that blow up an entire planet. The Death Star also could do this, although it does seem to be like some sort of freaky super weapon that would require huge amounts of power and people (maybe) to operate.
Size along is probably a bad way for the admittedly silly and pointless process of comparing sci-fi universes (something made more silly and pointless in that the interior universes are often inconsistent). I seem to remember on the original Star Trek series it is implied that the Enterprise alone has the power to devastate an entire planet, although certainly not blow it to pieces. As the series evolved, and possibly from episode to episode this ability seem to disappear. By Star Trek: Deep Space Nine, we saw fleets of what appeared to be hundreds of ships that were of (depicted as) smaller sizer then those in Star Wars. This was, obviously, due to increasing abilities of the FX.
Hmm...I'm just rambling. I seem to not have any opinion on this at all so I guess I will stop.