I've used a bunch of putters and the only conclusion I can come to is find one that you really like the feel of - one that just seems to fit your hand really well. Then putt with that and see how you do.
The Polecat and Birdie have really big rims (height-wise), so I'm not fond of them.
The soft magnet, rhyno, aviar, warlock, wizard, challenger and many others are very similar to me. If somebody said "you have to putt with this today" my game wouldn't go in the toilet regardless of which one I used.
It also depends on what you want to use your putter for. A wizard can be used for driving, upshots & putting, so it's pretty useful. The reason is it's stability. I carry a Warlock for putting and straight shots and a wizard for headwinds and longer drives.
I know many folks that use the aviar and challenger the same way. I used to throw a soft magnet, but while it's great for up shots and putting, it's a little funky for me to drive with since it's so much softer than the other dx type plastics.
You also have to figure in your putting style - do you hyzer putt, flat putt, anhyzer putt, pitch putt, etc. Each of the discs will vary slightly depending on the style. A wizard will come out of an anhyzer much stronger than, say, a warlock or a rhyno or soft magnet.
I used to throw straight on with a soft magnet, but now have switched to a pitch putt and find the stiffer putters just feel better since they don't give when I pitch them.
I do recommend (also) that once you pick a putter, grab several so that you can practice a lot. Putting with 4, 5 or 10 putters is a lot more fun than with just 1 when you are practicing.