Does anyone know he quickest way to marry an illegal Mexican immigrant and apply for citizenship?

My boyfriend and i would like to marry but he is illegal. Everything that we research as far as applying 4 citizenship seems 2 take 4ever and none is guaranteed of course. So i would appreciate insight, maybe a story from your own experience? I would just like 2 get an idea of whether or not there is a MORE simple way, or the least complicated... We realize that we can marry here while he is illegal but we do not wish 2 have it biting our behinds later... What we have researched is going 2 live in Mexico and apply 4 a fiance visa which could take up 2 six mths 2 approve or deny. Or marrying here and applying, with the request 4 pardon ( 4 him having been here for yrs already), and if this is denied, he will be unable 2 apply again for 10 yrs....