It's hard to pick...I like the ones with personality.
Justice Jackson for his opinions, and the fact that he swanned off to Nuremburg for a term to prosecute some Nazis.
The 1950s-era Courts were the best, IMHO. Minton, Reed, and Burton were known as "The Battalion of Death" because they so rarely voted to overturn convictions. Douglas was a womanizer and married a woman 40 years his junior. Black was a former member of the KKK (for political reasons, IIRC) who had a long-running feud with Jackson. Frankfurter used to write these long memos harassing his colleagues about deciding things too broadly, and would talk for hours during conferences.
I rarely agree with the man, but I like reading Scalia's opinions; he's a funny guy. Alito occasionally brings the chuckles -- his recent Jones concurrence was kind of hilarious.