No preference. I was into Trujillo before I even knew of Newstead, and pound for pound he is probably the 'better' bassist. However, I also feel as if Newstead is underrated in his role in Metallica. He was Metallica's workingman bass player. Ask this, on any of the Trujillo albums, is there anything that really stands out as being ROBERT TRUJILLO?? I haven't listened, but I doubt it. He's less likely to rock the boat creatively speaking. Ages ago watching the some kinda monster thing, it was obvious to me that Newstead didn't get any say on anything, and maybe wasn't being compensated enough to be in that role. He wanted to do something different, and it wasn't going to happen in Tallica.
I like to think of what could have been with Cliff. More complex lead bass playing, with even more devastating Fuzz tone with Wah... Imagine if you will 'Enter Sandman' with Fuzz Wah playing the iconic line.