I use them both. UESP is good for lore and looking up groups of items or what's in the game. TES wikia isn't as good with the lore, but their pages for quests and items are more detailed and their items have their own separate pages, instead of just being grouped into one page with no information or how to get them.
Yeah. Plus UESP doesn't have ANY pics of each item. I was trying to find the "Adept Hood" on UESP to try and find the base item. UESP gave no info at all. Wikia at least gave a little bit of info, however, none of it help me much.
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Seriously though, I use UESP for almost everything. It has info all around. Plus the Wikia changes its name every time a new game is released. Morrowind Wiki --> OblivioWiki --> Skyrim Wiki, etc. and has tons of pages that link to themselves... :facepalm: