the strongest was barragan luisenbarn, not in term of brute strengh but abilities... all espadas represent causes of death, and according to barragan himself he represented oldness which is the number one mortality cause... tough he was defeated easily by hachigen, he was because of his own power ("absolute one"..)
it depends ; shorter anime are good because you go straight on the action/ intrigue, but some times they end up too quickly and you stay unsastified (i.e tenjho tenge...); longer' ones never end and you have to wait numerous fillers to get back on the main history -such a torture...- that's why i'm going to say shorter' ones (if the end isn't dashed off...)
Japanese subbed in english... i think that when you dubbed a serie (no matter if the dubb is good or not), you loose some interest in the anime (for exemple the intonation of the character's voice when he is facing a danger, or when he is intrigated or surprised...). and after watching several animes your eyes become trained enough to be able to both read the subs and watch the image...