For vita, It really comes down to, does the game have to be a physical cart?, if so DW8CE is your only option as the other 2 are DL only. (and dont get DW Next even if it is physical) Also note DW8CE did have framerate issues that arent present in the other vita games, I cant remember if this got patched though (I played it on PS4).
if having a game as a dl isnt an issue then it comes down to what setting do you prefer, chinese history, japanese or mythological lore with chinese and japanese history on top.
Orochi is a somewhat dated game (the Dynasty Warriors characters are based on their DW7 counterparts, and Samura Warriors is based on 3) but due to its a cross over the number of characters exceeds over 140. And Orochi does boast the biggest amount of content in any warriors game to date by a huge margin.
SW4 due next month would be the most polished of the 3 games (I prefer SW btw)and it's the only series with VN. The 3ds is more of a side story invoving a charcter you create that participates in famous battles, where as this is more historically accurate (but not completely accurate, it is a game after all).
honestly if you can try and play all 3 though spread it out otherwise you can burn yourself out on warrior games if played too much (just like any game) if you just want fun factor and content i'd edge orochi but Samurai Warriors 4 will be the most up to date and polished game yet.
I should add DLC for all 3 games, DW8CE, Samurai Warriors 4 and Orochi is crossbuy between the other versions of the same game, so dlc you buy for say orochi vita gives you that dlc for the ps4 version too.