Diesels cleaner than hybrids?

There is no single solution.
Unfortunately, the government has provided incentives for hybrids in the form of tax breaks and illogical HOV special treatment while at the same time adopted regulations that stifled the diesel market for passenger cars and light diesel vehicles in North America.
Emissions regs. were raised to levels that were not practically attainable in the time frame they were enacted and sulfur in the diesel fuel in US made it the filthiest diesel in the world.
Diesel, natural gas, electric, hybrid, hydrogen and other technologies should be supported by regulations, not restricted, and the free market will fund the market, not government tax incentives. Let the government build the roads, not decide what vehicles we purchase.

It's well known that diesels are good with CO2 emissions, that's why Europe encourages their use through fuel taxes. The reason US-based policies don't is because they're bad at particulate emissions which cause smog and immediate health effects (immediate relative to potential global warming). You can taste the difference if you walk around a European city...
 
Diesels are also worse with NOx emissions, which come in much smaller quantities than CO2 but have a stronger global warming effect on a molecule-by-molecule basis.
 
CO2 emissions aren't everything.

If you look at how much vehicle-out emissions have been reduced since we started regulating them ~1970, you'll see improvements on the order of 50-100x, or 5000-10000% on all regulated emissions (CO2 was never a regulated emission). In that timeframe, the US 'fleet' has only grown 1.3-1.5x (I've collected data, but not in front of me). As of 2006, all diesels have to meet the same emissions requirements as gasoline vehicles in all categories, including NOx and PM. There were several 2006 diesel models that did this, without any appreciable aftertreatment. In fact, 2006 diesels with minimal aftertreatment were meeting emissions levels corresponding to 2003 gasoline versions of the same models - not too much of an emissions gap. In my opinion, 2006 emissions levels, representing a 50-100x improvement over 1970 levels are good enough considering the fleet size and total # miles traveled has only increased 1-2x. Regardless if you agree with that or not, if US emissions regulations continue to be more stringent than the rest of the world's, even if only slightly, we will never enjoy their advancements. Not many companies will be willing to invest huge money to develop diesel aftertreatment, for instance, to meet more stringent US regulations with their 1-3% diesel diesel market, when they need to be developing technology to meet Europe's evolving regulations with their 50% diesel take rate. For diesels to prosper in the US, we'd be wise to adopt Europe's emissions regulations, and follow their exact schedule for improvements (Euro5, Euro6...).

CO2 causes long term climate change over decades.
 
Particulates cause smog and lung injury today.
 
The US EPA is more concerned about today than 10 years from now.
http://www.fueleconomy.gov/ clearly separates climate changing pollution from instant air quality changing pollution.

The diesel xcars are really more reliable and efficient than nay gas engine. It is so unfortunate that the Auto Parts Makers doesnt' infom the public enough why the presnt deisel engine is not only cheaper in use but also reliable and greener.