NJPW, AJPW, and NOAH are historically the top promotions though Wrestle-1 is starting to make a name for itself thanks to the backing of Keiji Mutoh (aka the Great Muta). If you're looking for a place to start, let me recommend a few matches to you...
Yuji Nagata vs. Hiroshi Tanahashi (from February 19, 2006)
- Tanahashi is basically the John Cena of Japan, you may also know him from some of his great matches with AJ Styles, Nagata is a veteran that had a few brief appearances in WCW, this match is where Tanahashi was 'put through his paces' if you will
Prince Devitt vs. Kota Ibushi (any)
- Devitt and Ibushi are both breathtaking, with luck we will get to see Devitt perform more great matches within WWE but he already has many great matches under his belt and few match the quality of his bouts with Ibushi
Shinksuke Nakamura vs. Shelton Benjamin (?)
- Not certain what the timeframe was but I'm sure you're familiar with Benjamin and this is him taking on one of the top stars of the modern era in Nakamura, who at one time was the greatest wrestler on the planet in my opinion
Manabu Nakanishi vs. Minoru Suzuki (October 9th, 2004)
- Two future legends going at it, a fairly basic contest that gives you a good idea of what they are both about...Nakanishi is famous for following the same workout routine that the Road Warriors did and Suzuki was an amazing MMA fighter in his time
Kenta Kobashi vs Mitsuharu Misawa (October 31, 1998)
- If you're looking for two of the top names in Japanese wrestling history going at it then this is a must see, Misawa tragically passed away a few years ago and Kobashi was forced to retire due to nerve damage to his arm, but they will both live on forever as two of the greatest competitors in wrestling history
KENTA vs. Takeshi Morishima (March 4, 2007)
- If you're wondering what the big deal is about KENTA, watch him face one of the biggest beasts in Japan and see how insanely strong he is for his size
I think that is a good starter to give you an idea of who you want to check out and which events you may be most interested in buying