I have been using NMTs (Popcorn Hour A110, A-200) for the past 2 years now and my brother has a WD-Live. I can confidently say, NMTs are the best HD Media players out there. It plays even Blu-Ray from a folder dump and if I have the Blu-Ray ISO then thing even gives me menus. Add to that it can play Youtube, Internet Radio. Torrents and Rapidshare downloading are like icing on the cake. Suffice to say I very rarely use my PC for downloading or watching Vidoes.
My A-200 plays a content rich blu-ray hitting 80 mbps (most 1080p MKVs max out at around 20-25 mbps, blu-rays hit 80 and sometimes even higher) during heavy scenes over LAN (the .m2ts or blu-ray ISO is on the comp) while my older generation A-110 couldn't handle those extremely high bitrates.
One good test is to try and play a 500 mb Samsung demo video (Aquarium) which is so rich that most HD media players struggle to play it (Xtremer, Asus). If a player can play that comfortably than it can probably handle anything you throw at it.