I guess everyone who has done a bit of work on various machinery has their own preferred methods when it comes to shifting stubborn fixings and at the end of the day it is whatever works with the tools to hand.
Personally, I am a big fan of socket type hex (Allen) drivers as the hex itself tends to be a better fit (unless you have some really good quality T-bars or Allen keys) which in my experience is the most important thing, plus you can then choose a breaker bar of appropriate length to loosen it.
If I still have problems then my first port of call is a good old fashioned Impact Driver which you can give a thump with a hammer and by taking the Hex adaptor off reveals a 1/2'' square drive to pop an impact socket on.
I did buy this jobbie (about £40 off eBay) a while back when I changed my clutch but with an un-adjustable claimed torque of 450Nm it's not very subtle and I wouldn't use it on anything less than M10 (17mm hex head) or for doing anything up with.
I prefer Aluminium bolts for casings and non-safety critical applications and am not keen on Stainless bolts into aluminium engine casings as they are quite brittle and so once corroded (lets face it- how often does anyone remove them to clean or re-grease between needing to?) if/when one does break, I know which material I would rather be having to drill out.
Again with using copper grease, there is a school of thought that it can actually make things worse when using two different metals through galvanic corrosion but I am not an expert on such things by any means.