I think many factors make TIL the best site out there for TES fans who already have above-average knowledge of the lore, and who want to expand their understanding. But the UESP is definitely the place to go to get your bearings on the lore, and I think you'll also find it reliable for game help, news, etc. It's been around for a long time, and it is the most comprehensive compendium of knowledge regarding The Elder Scrolls out there, bar none. Once you have a grasp on the namespace arrangement, you should have no problem finding reliable information on whatever you wish.
Just keep in mind that most http://www.uesp.net/wiki/Lore:Main_Page pages have been improved a great deal in recent years, while a handful have been criminally neglected and may be lacking info. Look for references, summary boxes, etc.
The TES Wikia site kind of seems like a train wreck. No offense to the users, many of whom I know to be friendly and knowledgeable folk. But it's had a relatively great amount of misinformation and gaps in coverage on its pages, they've had one or two administrator controversies recently, and plagiarism of UESP content has been a concern since its inception.
And, this is just my personal experience, but whenever I check on the TESWiki now, it's primarily a bunch of people doing roleplays. I don't know if they have a lot of dedicated users out there trying to make updates for ESO. The UESP is not free of problems, but the ESO coverage has been slowly coming together, including lore coverage, even while people continue to improve the Skyrim section. Heck, there are still editors perfecting the Daggerfall section there. The active editors are incredibly loyal to the project and are polite to a fault. Literally, I fault them on their politeness. One of the veteran users recently lost his patroller status and got temporarily blocked for being I would consider slightly impolite as a result of a disagreement with a new user. You can be sure that you will be treated with complete and absolute courtesy by everyone at UESP - or else.