Heavy metal any day of the week, while there might be more quality thrash metal bands than NWOBHM bands the bands that are good are really fucking good. I'll listen to Maiden or Judas any day of the week over the majority of thrash metal bands.
Thrash metal, can be very monotonous and boring, and many old thrash bands turned into mainstream acts (as Metallica), but the genre has something that make it better than traditional heavy metal, thrash metal is fast and agressive, is a perfect genre for concerts.
About NWOBHM and traditional metal, I love traditional metal, because is not as heavy as thrash, groove, power, or any other non-extreme genre, but it's still a heavy genre. I love the guitars in all the Iron Maiden songs, and in Judas Priest songs as well, I like the riffs of Black Sabbath's s/t, they are like a heavier blues rock, and the riffs of Paranoid, War Pigs, Sabbath Bloody Sabbath, Heaven & Hell, ect, are awesome, Thrash metal doesn't have a lot of original riffs, thrash is more generic than heavy metal actually.
Voices in thrash metal are harsh and usually are shouts, most of the classic singers (Ozzy, Halford, ect) doesn't shout, they actually sing trying to stick to the song, trying to make harmony, thrash metal doesn't, it's more about speed and agressiveness than harmony and melody.
It's hard to compare those genres, both are very different.