It's impossible to choose one best episode because there are a mass of them and they are nearly all astonishing.
I've picked a few I think best episodes ever:
- Top Gear - [2x4] - 01.06.2003 (Jag episode)
- Top Gear - [3x1] - 26.10.2003 (BMW 5 & mule GT40)
- Top Gear - [3x2] - 02.11.2003 (Isle Of Man)
- Top Gear - [3x6] - 07.12.2003 (Superb Vantage test & Monaro)
- Top Gear - [4x1] - 09.05.2004 (DB9 vs TGV)
- Top Gear - [4x8] - 18.07.2004 (Quattroporte & GT40 & Rover V8)
- Top Gear - [5x4] - 14.11.2004 (Zonda & Vanquish)
- Top Gear - [5x5] - 21.11.2004 (Morgan & Nurburgring test)
- Top Gear - [6x3] - 12.06.2005 (Amazing photos is TVR test)
- Top Gear - [7x1] - 13.11.2005 (Ascari & Isle Of Man)
- Top Gear - [7x2] - 20.11.2005 (BRG & Fabuleous RS4)
- Top Gear - [7x3] - 27.11.2005 (3 Supercars)
- Top Gear - [Winter Olympics] - 12.02.2006 (One of the funniest eps)
- Top Gear - [8x1] - 07.05.2006 (For mezmorizing Koenigsegg)
Wow, I've made a huge list but those episodes, for me, are the best of the bunch, there is also a different feel in the series 1-2-3,4,5,6-7-8, I mean 1-2-3 feels a bit old but it was the first, 4 felt very soft and pleasant, 5 was fully a tyre shreding petrolhead show, 6-7-8 got a bit too monumental I think, different from the others but still mindblowingly good.
Thats my personal watching-TG wierd stuff and I'll be surprised if someone shares my way of thinking but you never can tell. 8)