i dont know what to buy for losi 8 buggy..

[BrianG]

Any of those motors will be fine. The CC2200 might be too powerful/torquey for a buggy on the track. The CC2650 might be too fast unless you gear down. The RX8 2050 would probably be just right power and speed-wise.

Another option is Castle's 1512/1.5y (1800kv). Might be a tad slow on 4s depending on your gearing options, but is ready for 5s or even 6s if you choose at a later date. 5s would be the sweet spot on this motor IMO. And if geared for reasonable track speeds, should provide relatively low current, which helps efficiency and runtimes.