Hmm. It looks like a kind of trade-off between the two methods right?
At first, I thought echoing custom style block directly to the header may not be a good way because the page would look too messy and, you know, kind of unorganized way to do so. But I never realized the fact of the performance as @pixelentity mentioned. That's very great to know.
I just tried the method of "special" style file like style.php and that works perfectly too.
This is quite questionable for which one is better..