Since the Tier 4 was brought up I'm going to go against the grain. Our S770, new T770 we bought this Summer to replace the T750 and the T770 I have coming to replace the Tier 3 emissions machine I run aren't bad since they just have a DPF but no Urea. Urea is a PITA and I hate the idea of having another fluid to keep track of. The T770 that we have that is tier 4 has 350 hours on it and has only had to regen for 1.5 of those total hours. Not too bad. The piezo injectors that are coming into the industry also help with fuel atomization and fuel consumption.
Sometimes in the morning the last thing I want to smell like is burned diesel. The sweet smell from DPF treated exhaust is actually nice when I have to be by it.
I'm about the last person to agree with more emissions BS because of the costs but not getting a headache is a nice change.