Procharger D1SC: Street manners are very nice. It builds power down low and keeps on going. The 4.1 drive ratio of the supercharger helps to build power fast. The faster it spins the more power that comes out. Think of it as a hybrid between a centri and pd. A belt driven turbo. Comes from the factory as a blow through and with a high rpm billet wheel.
Paxton: Nice street manners, lots of power up top. For lack of a better term I'll say it just doesn't "spool up" as fast as the procharger due to the 3.6 drive ratio. It's also not an apples to apples comparison because the D1 can move 1400 cfm while the Paxton SL moves 1200 cfm max. A better comparison would be the bigger Paxton/Vortech (2000 and ysi?). Still, the Paxton is a great value. IMO it needs to be converted to blow through to get the most out of it.
Whipple: My experience was that once the power got above 525 or so the street manners were gone. The nice thing about a twin screw is also the bad thing about a twin screw. That thing is it builds max boost as soon as the bypass closes. It's great for instant torque but once that torque gets above a certain number you have to drive like grandpa around town. Just a little too much throttle and you are putting 500rwtq to the ground with the expected consequences of spinning the tires. My best experience with the whipple was around 500-525 rwhp. The Ford Racing calibration is fantastic and keeps power around 475rwhp which is very useable and street friendly.
The one form I haven't tried yet is a turbo. If FRPP releases a kit for the 2012 Focus I'll probably put it on my Focus. Lots of room in the engine compartment.
The reality is they are all good and all have a niche in the performance market.