That would depend on what your meaning of friendly is? Eco friendly?
Here is a link to 2015 Best Engines from Wards- http://www.autoblog.com/2014/12/10/wards-10-best-engines-2015-winners/
Is there a certain 4cyl engine you are inquiring about? I will be happy to send over pros and cons?
〉 Answered on Feb 16th, 2015 by Julie Kimes, General Sales Manager at O'Daniel Automart / O'Daniel Mazda