People who prefer Second life over IMVU are like vegetarians (the self righteous kind. no offense meant to any vegetarians out there).

And what I mean by this is, if IMVU is brought up, they express their opinions whether it was asked for them or not.
Much like how many vegetarians will bring up the fact that they are vegetarian at even the vague mention of meat.

If someone posts a screencap from IMVU (or something else IMVU related), there will always be that one person who has to comment "Second life is better" "IMVU sucks" "IMVU is just a bad copy of Second life" or something else along those lines.

I'm going to say a few things...

1. No one asked if you preferred SL over IMVU
2. No one cares if you prefer SL over IMVU.
3. In fact, no one brought up SL at all.
4. You are not special for preferring SL.
5. It does not make you 'cool' to bash on things that don't match your taste.
6. In fact, you just look like a douche when you do that.
7. Yes, you are entitled to have opinions, that does not mean you should shove them in people's faces.
8. Opinions are opinions. Not facts. Remember this. "good" "better" "nicer" are, for the most part, opinions.
9. Wrap your head around this: people are allowed to have opinions that disagree with yours. *gasp!*

Now disclaimer:
While I have yet to see an IMVU user do this same thing about SL, I fully acknowledge that it probably does happen.
It is just in my experience that I almost always see the SL people behaving this way.