Lego mindstorms biotic is the best selling set ever made. It has sold over 1 million.
I think the best selling LEGO ever made is the LEGO city edition.
The best selling Lego set in 2014 is the Desert Skiff. It was created in 2012 and averages around $25 in the store and online.
medieval market village
One may purchase a Lego train set online through Amazon, Ebay, Craigslist and Shop Lego. Other ways to purchase a Lego train set online is Cymax, and John Lewis.
medieval market village
Lost city of Atlantis
It is truly up to you to decide which set is the best.
The best place to find the Lego Monorail set is on eBay. These sets are quite expensive and cost over $150 each. There are also many listings for parts for the Lego Monorail set on eBay.
lost temple
I would say the Titanium Command rig is the best set even though it's pricey...
LEGO set 8631 is LEGO Agents set Mission 1: Jetpack Pursuit.