I opted for the L2501 over the L3301 based on simplicity. The L2501 has no computer and no diesel particulate filter. It is probably as simple as a tractor gets today.
However, in the interest of full disclosure, the simple L2501, designed to skirt Tier IV emissions requirements, (legally) spews a lot of diesel particulates. According to those more knowledgeable than I on emissions, the L3301 with a Tier IV diesel particulate filter/incinerator spews less than 1% of the pollution load of an L2501 with a traditional, low-tech muffler.