Filters for Protecting Lenses: High-End vs. Budget vs. Dirt-Cheap

With digital photography, using filters to achieve special effects has become much less common, with the exception of neutral density filters, graduated ND filters, and circular polarizers.  The other exception, with some controversy, is the use of filters to protect lenses.  Typically, UV filters or sometimes skylight (warming) filters are used for this purpose.

In this post, we compare images from lenses without any filter, with a budget filter, and a high-end filter.  The filters I tested were:
(a) a high-end filter, the Hoya HD Hardened Glass 8-layer Multi-Coated Digital UV Filter, around $70 for 77mm.
(b) a budget filter, the Hoya skylight filter (standard version, not multi-coated), around $20 for 77mm.  Note: the skylight filter has a warming effect, so for purposes of this comparison, please take that into account as part of the filter design and not an inherent characteristic of budget filters.
I've also included a separate test for an ultra-cheap generic UV filter.

I tested the filters on two lenses:
(i) a flare-resistant lens, the Nikkor 24-70 2.8G on a Nikon D3; and
(ii) a lens that is [supposedly] susceptible to flare and ghosting, the Tokina 11-16 2.8 on a Fuji S5 Pro.
Both lenses use 77mm filters so I was able to use the same set of filters for the tests.

Hit the jump for the samples.