As far as I know, the two sets of endings are equally used in Spanish, but the Mexican people I know never use the -ese/ -ase endings.
I personally much prefer the -ara/ -iera endings, but my teacher would rather I used -ese, to be sure I'm not using the future tense instead of the imp. subj. I however, want to avoid things like sintieses, because that sounds strange to me.
He says use whichever, as long as you stick to one.
My question is, essentially, which do you prefer to use (and what kind of Spanish do you speak)? Is there any difference? Can you mix and match -iera with -ase between -er/ -ir and -ar verbs?
Any help you can give me would be thoroughly appreciated, as we got ourselves into a real semantic dilemma! Thank you.