There are of course exceptions but for me, short samples work better and long samples are shit. I didn't like the Nystagmus album or Talpa's people are animals. I didn't like the unsane sample at the start but loved the one word sample later in the track.
I agree with what you say about understanding the sample. I like more, foreign language lyrics if there are any. Puff Drangon - Sazanami
Longer samples maybe go better in more chilled out music but I much prefer it when it's not too prominent like in Tripswitch's Deer Park at the beginning. And Banco De Gaia had a nice story at the beginning of China (clouds not mountains)
Of course any sample long, short, english, johnny foreign or whatever can work but it has to really be the perfect sample for the track. Far too often you here a sample you think is quite cool at first but then after a few more listens you just wish they would have missed it out.