Tenchi in Tokyo was the worst alternate universe hack job to an original anime series I have ever witnessed.
The Universe series is my favorite, but many argue the OAV is superior. The real differene IMO is how the writers treat Mihoshi. She is a ditzy bimbo in the Universe series, while she just a lucky clutz in the OAV. Universe gets my vote because Kiyone is actually an integral character, where as she doesn't appear but in one brief instance of the OAV.
The three Techi movies are superb. None follow the Tenchi in Tokyo plot. It is hard to decipher just what series the movies follow, but most would say 1 and 3 are Universe, while 2 closely parallels the OAV.
The facts:
Tenchi Universe: 26 eps, 2 movies
Tenchi OAV: 6 eps
Tenchi OAV2: 6 eps
Tecchi OAV3: In production (not sure if completed yet)
Additional:
Tenchi GXP: 36 eps (Not really related to original Tenchi series)
Pretty Sammy: 3 eps (Spoof of "magical-girl" animes)
My anime? Local stores, online stores, and a little known search engine.
http://www.noated.com
Hope this helps,
Robert Richmond