They're all basically the same until '03 when LOTS of changes were made. If I had a choice, I'd do a '02. The cam chain whine was eliminated and the valve covers don't seem to develop the leak that the '00 & '01 do. They also had a slight bump in power due to a revised airbox.
If you get an earlier one, make sure they check the pass. side valve cover for leakage and when you test drive it make sure you run it hard (near redline) for a while and then sit at idle with the blower running to see if you can smell burning oil. That's the tell-tale sign of a leak. It's a common little leak and they will know about it at any LM dealership, but they also will bank you not finding it. It's not a concern for durability since it's such a small leak but it stinks.
Bottom line, NONE of the LS had/have engine problems other than those leaking gaskets on the early V8s.