I’m going to start a series of polls where I see which version of songs with 3 or more renditions by CW people prefer. Siúil A Rún is a classic and I’m curious to see what everyone’s favourites are!
NOTE: please keep in mind for all of these that I don’t have any of the DVDs (yet) and haven’t been to any concerts (yet) so although there’s probably some special version they did with Alex, Muirgen, Hayley, and Mairéad Z (the secret lost member only the real fans know about), I’m going off of somewhat limited experience and these are the only versions I know of so far. 
Personally, my favourite version of the song is the original from the debut, but I love all of them and feel that they each have different things to contribute!
The original is very catchy but still maintains the sombre tone of the lyrics, and Órla’s voice is incredible! 
Órla’s solo version is beautifully ethereal and feels the most sincere of all of these; I also love the whistle in the background.
The Destiny version is a bit too cheery but an excellent showcase of the vocal talents of Mairéad C, Susan, and Éabha, and how they work amazingly together, and Máiréad N’s fiddle is enchanting as well. I also love the harp in the background.
The Ancient Land version shares the same problem with being too cheery (though that is mainly the problem of the background arrangements), but Éabha’s voice is wonderful and Tara’s harp is incredibly catchy! This song is permanently in my brain, especially the introductory harp.
Anyway, I’m curious to see what you all think.  

 I have a feeling that either the Destiny or Ancient Land will win, but I could also see some older fans choosing the original. I’m not so sure if anyone else knows about the one included in the compilation album, but I think they included Órla’s solo edition as a bonus (they did the same with Walking In The Air for Chloë).