I personally liked the refuelling era best.
Refuel and change tyres whenever you want, get different stategies, short fast aggresive stints and the long game conservative stints and all those inbetween.
Slower cars able to start ahead of faster cars (alonso pole position Hungary 2009).
I also liked 2010 mode, for the fact that drivers needed to have outright pace and the ability to manage tyres, one without the other wasn't good enough.
2011 - 2012 I do not like as much, driver speed is not much of an advantage now, its supposed to be racing and yet you have too be too careful to get into a race