I love P-90s, and have tried several. The soapbar in my 59 Les Paul Jr. sounds incredible to me, but is pretty noisy. Years ago, pickups weren't produced very consistently. Some were killer, and some were mediocre. As far as replacements, I've had Thorns, Fralins, Duncan's, and Lollars. They all have their own vibe. If noise is a concern, Lindy and Ron Thorn wind amazing P-90 humbuckers. Neither are remotely close sound-wise to those lifeless Gibson P-100s. Lindy's sounded like great P-90s without the hum. The Thorns sounded like kickass humbuckers. The singlecoil Thorns sounded like Soapies on steroids. Great tone, but BIG. Singlecoil Fralins sounded closest to vintage to my ears. The Lollars I had sounded "sweet" although I know he can do different winds for different tones. The Duncans PRS uses are all (I believe) neck models. To my ears all of the "boutique" soapies sounded better than the stock PRS Duncans. HOWEVER...the Duncans sounded good. Very good. I'd be inclined to say the typical Duncan P-90 (and I've had 3 different sets) is probably better than the average (even vintage!) Gibson soapbar. Like I alluded to earlier, some of the vintage Gibsons sound absolutely amazing. But not all of them do.
As for other recommendations, I've heard guys rave about Throbak and Wolfetone P-90s, though I've never played either. They both wind awesome humbuggies though.