Fuera o fuese, hubiera ido o hubiesen ido
 

¿Por qué hay 2 diferentes conjugaciones de verbos en el imperfecto y el pasado perfecto tiempos?

Imperfect I went, was going fuera fueras fuera fuéramos fuerais fueran
OR fuese fueses fuese fuésemos fueseis fuesen

Past Perfect - Pluperfect I had gone hubiera/hubieras/hubiera/hubiéramos/hubierais/hubieran ido
OR hubiese/hubieses/hubiese/hubiésemos/hubieseis/hubiesen ido

Es regionales? España versos América Latina?
Que es el preferido o más comúnmente usado?

Como siempre, gracias.

You can use both of them equally. People in some areas of Spain tend to use the second conjugation more often, but you'll hear both used.

In Latin America, the first conjugation is used more often, but again, you'll hear both.

Listen to what the folks around you are using and mimic them.

The best piece of advice I can give is that you always use the -ra* forms and know both.

At least 85% of the Spanish speakers use the first form almost exclusively. The second form is used almost excluding the first form only in Southern Spain and Canary Islands (...and maybe the Central Valley in Colombia?)

Besides, there are some uses of this tense that are correct just with the first forms, although everybody will understand in the case the second form is used.

I use the second form to avoid monotony -Spanish abhors repetition- when there are many verbs conjugated in imperfect subjunctive in the same phrase (and a lot of educated speakers everywhere do this as well).

"Si pudiera, podría, pudiese..." is a phrase used here to reproach someone who is talking too much in a speculative fashion but what they say boil down to excuses.

Gracias, otra vez. Poco a poco estoy aprendiendo mas.

Thanks aleC, I'll add that one to my list. Very useful!