I think, for some reason, that the fact ew think the bugs are so easy to defeat are because we have the experience taking cats out. At least most of us have that experience. WC2 seems to be the toughest game (I think) out of the Kilrathi trilogy, and if you can fly and kill Cat Cap-ships in WC2, you reaqlly should be able to do the same in WCP. Only difference in WCP is that the bugs have the shield gens that you need to take out first.
Now, if you began your venture into this series with WCP, and were killing bugs for a long time, then decided to go back to WC4 and WC3, then you might find killing the cats easier than killing the bugs.
Another thing to consider is the fact that Confed technology has gotten ALOT better since the origional Wing Commander. In the first game, a fighter like the Rapier was the kick-ass ship that everyone wanted to fly. Actually I preferred the Raptor, but that's just me. Anyway, back onto the topic, The Arrow of WC3 could fly circles around the Rapier and literally rip it apart from the seams (granted, the issue of pilot experience may come up here, but for argument's sake let's just go with both pilots are equal in abilities and experience). In WCP, Confed tech is so advanced, it's not funny. With the tech we have in WCP, we could have ripped through the Kilrathi in a heartbeat. The bugs were advanced, but we did steal some of their teech as well and incorpirate it into our own weapons. With the cats, we had to use rugged, multi-purpose equipment.
So as for the origional question of who is tougher, I can't really say for certain. I believe that it's like comparing apples and oranges, two completely differant things in two differant circunstances and enviroments.
Against the cats, we were in the middle of a war with rugged, makeshift and not-so-high tech weapons and against the bugs we had the high-tech (and shiny) equipment of a somewhat restored Confed.
Just my thoughts,
-=DeltaKiller=-