Just do whatever you want and whatever YOU think looks good. I do both defaults and brushed sigs and I find that oftentimes it takes longer and is trickier to get a good looking bg with brushes. At the moment I'm moving away from brushes, though I still like to mix it up and combine styles and such. What I'd like to know is who decides what's 'in' and 'trendy'....and why it matters *rolls eyes*
I guess it becomes trendy when you make things ppl just like to see and not what you like to do........I really dont kno....but do what the F**k you want its your sig your style.
I used to use brushes when i first started out it really was extremly simple, click a couple times, color it, stick a render in ur done, but that's boring, i only use filters and default PS tools now, it's more of a challenge, and my BG isn't someone elses work.