According to the replies from Shark customer support, the Dust Bin Capacity is the only difference between Shark NV44 and NV22/NV22L, the Shark Shark Navigator Deluxe Upright Bagless Vacuum NV44 dust cup double the capacity of the NV22/NV22L.
The Shark Navigator Upright Bagless NV22 and NV22L are exactly the same machine, however, their colors are different, the NV22 comes in blue while the NV22L is in lavender color.
If you care about the accessories, here is more detail about the tools. The NV22 (sold at walmart) has only 2 tools: a dusting brush and a 5.5″ crevice tool; besides these 2 tools,the NV22L may come with a pet power brush, or a pet power brush and a 24 inches crevice tool, depends on where you buy. Some may include the 24″ crevice tool while others may not.
The NV44 comes with a pet power brush, dusting brush and the short crevice tool.
Shark official site sharkclean.com does not prodive any info about the NV44, such as specs, accessories and manual pdf download link, so you’d better contact their customer support for requiring any info you want to know before buying one, in case some parts need replacement or anything similar. If they do not sell the replacement parts, that will be a problem.
If you like the large dust cup, you can also have a look at the NV70 or NV80, they have even larger dust cup than the NV44.