welll, here's a few things.
very few people give an informed opinion on putters because
1) most people are bad putters
2) most people have only thrown one weight range of putter
there's also a few aspects to look at putters
1) as a putter
2) as an approach disc (think wedge)
3) as a short driver (7-9 iron)
honestly, i don't think any one weight is best suited for all 3 of those.
assuming you pick a stable putter mold (there's only like 5), then it's easy to break down.
heavier putters are SLIGHTLY (only slightly, i cannot emphasize this enough) better into the wind, but are worse if you nose down putt and any putt with a tail wind.
heavier putters ARE better as drivers.
mid-weight putters make the best approach discs since they have added stability but also are able to be thrown with a very compact flick/chop stroke and still get decent carry (heavier putters are not good for this).
lighter putters will carry farther when thrown with the same power as a heavier putter. on longer putts, this is significant. if your putt is flat (read as: you don't use any turn/fade or have the nose significantly up/down), a 165g putter will have about 30% more carry on longer putts than a 175g putter. i can putt a 165 45' and with the same power a 175g will go 35'.
heavier putters in slicker plastic will catch more on the left side of the chains than lighter weights, but lighter weights in slick plastic will catch more on the right side. in soft/sticky plastic, reverse this trend.
heavier putters will have more cut throughs, lighter putters will have more bounce outs (e.g. pushed out by chain reflex).
as for soft vs. hard putters:
soft putters will skip/roll less, but also will not hold as good of a line as a firm putter (soft putters flip more easily and are more low speed overstable). they also perform worse into the wind, unless you are throwing nose up and want a parachute drop type shot. soft putters catch more on right side, but miss more on left side.
needless to say, my putter rig:
175g med wizard - drives
171g med wizard - long approaches, finesse approaches
170g supersoft wizard - air bounce approaches, stuff where i need it to stop dead
165g - putts
btw, if you dont' like the kc aviar, you won't like the wizard either. the wizard is basically just a more stable kc aviar, but it is more difficult to putt with since it has increased nose angle sensitivity.