The problem is, there isn't a good answer. Each person giving you an opinion is going to be based on a couple of factors:
1. Personal Experience with their specific bike or motor
2. Connections they have with a shop selling a specific motor
Take your pick on the motors, but I'd stick with one that is 120-124cc's with a 4 or 5 plate clutch mounted on the primaries, with a 78.5 mm cylinder height. Lifan, Zongshen, GPX, etc. all make a similar motor based off the Honda Nice 110. Since they are all so new to the market, there is nobody with long-term experience with these motors to tell you that they have been holding up for 1 year, 2 years, 5 years, etc. They all make similar power numbers in stock form. All will need additional parts when adding Big Bore Kits, stroker cranks, etc.
Additionally, the market is changing so fast that what you perceive to be a good motor may already be outdated with a new shipment of bikes/motors that is coming in to the country as we speak.
Make sure you can get replacement parts, find a vendor who you are comfortable with, discuss the warranty, and make your purchase if said vendor will ship overseas unless you are just digging for information and plan on importing in your own stuff from China direct.
If you want longer term information, you are posting on message boards in the wrong country. You need to focus on Europe who have 1 year's more experience in this area.