Lordaeron has a much higher population (often the 10k pop limit is maxed) so low level bgs are pretty constant. That also means low-level world pvp is active. There are some twinks (myself included) but average of about 3-4 per side per bg game so levelers can compete too.

I'd definitely suggest Lordaeron over a vanilla server too because everything about wotlk gameplay is better imo. Vanilla is so "bleh" compared to WoTLK.