I am also a long time Lenovo ThinkPad fan who switched to Ubuntu. Eventhough I am successfully running 14.04 on my T520 right now, I too have been looking for a Mac alternative. So far, here is my potential line-up:

Razer: http://www.razerzone.com/gaming-systems/razer-blade

Dell XPS 15: http://www.dell.com/us/p/xps-15-9530/pd?oc=fncwx1602h&model_...