Personally, I think the Jansons is overrated and overpriced. The problem is that Jansons messes around with the music too much, adding things that aren't in the score. Some people like it, I don't.
My preference for a complete cycle is easy: Igor Markevitch on Philips. Two 2-disk sets have thrilling accounts of the symphonies, and you can get his Manfred separately. The sound is simply glorious even these 40+ years later. As a second choice, the Maazel/Vienna set on Decca still hold up really well.
If 4-5-6 is all you want, I'd buy the Ormandy's on Sony without hesitation. The Monteux's on RCA are also superb.
I haven't been too impressed with almost any Tchaik recordings in the digital era. The conductors just don't get it: Tchaikovsky isn't Maher or Brahms. You have to play with a certain exuberance and swagger and not over interpret them. That's why Monteux, Maazel, Ormandy, even Karajan work so well.
One Tchaik recording I would never be without: the 6th from Furtwangler. This is the stuff legends are made of.