Imperfect subjunctive....which option?
This is really for the average native speaker, but I'd appreciate input from anyone.
Which option of the imperfect subjunctive is used most by you or in Spain?
Thanks!!! 
4 Answers
There are studies on the distribution of these forms, which varies from country to country. In Spain they are roughly used the same, and in most parts of Latin America the -ra form is much more used in spoken Spanish, but the difference is not so significant in the written Spanish. The preference of one form over another also depends on the register used by the speakers. Don't over-analyse it, and stick to just one of them.
I have observed that in the last 20 years most people tended to use - iera forms and leave aside -iese forms.
I don´t know if someone else has experienced the same, but I like to use both forms indistinctly, and to use them frequently since subjunctive itself is falling into oblivion.
Maybe because people is systematically brainwashed to accept dull reality and facts, so using language forms that might help you to reflect on possibility, probability, likelihood and options is almost a linguistic terrorism action. 
If you mean ra or se ending, then it has been said here many times that the ra ending is more common. (not a native)
Another imperfect subjunctive is often seen in literature; for our present purposes it is used in the same way as the -ra imperfect subjunctive, and is formed the same way, by using the preterit third-person plural minus -ron as the stem, but using -se endings rather than -ra:
Delete.
