You guys are all pretty funny.
There really is only one choice for blowers and that is the MPx.
Previous versions (MP1, MP2, MP3) are all outdated and the S-port is the same as it always was. Any of these blowers are typically going to come at you used and will make a good upgrade from stock. The MPx is the only new blower package that can be bolted on and run and it can make up to 400rwhp with readily available 25% OD pulleys.
Other blowers are all custom and do not represent something that someone can simply "choose from". You can get a Procharger, Vortec, turbo, AR, Whipple, M112, M122, or hell you could put a B&M 471 if you want on the motor but in each of those cases you will have to either make it yourself or convince someone else to make it for you. None of this is any different than it was 10 years ago.
With the way that M90 blowers and parts have held their value it only makes sense to buy what is readily available so that you can enjoy your car with up to 400rwhp now and if/when you make a deal with someone to build you a custom kit or you figure out how to do it on your own then you can sell your M90 for 75% of what you paid for it allowing you to have your cake now and later too.
The people who have anything other than an M90 have waited a long time and have had to put up with the kinds of things that are typical for a custom application. I guess if there is a special "handshake" and "ring" it would be known as "patience" and "$$" because that's the biggest difference between an off the shelf M90 and anything else.