380 class motor is popular among smaller RC cars and boats. However, 380 is easier to get overheated and is less capable torque-wise. 390 is longer and has more torque.
390 is increasingly used but there are just too many variations. Some will not deliver anything meaningful unless under 12V or 3S, which is not possible given the limitation of most brushed ESCs.
The photo below shows one (390-6221) which is very powerful even with 2S power. 
Another one which is pretty good under 2S is 390SAP 5024.
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