What's your attraction to each gun? And which 226 Blackwater? There are two models of the BW from Sig, the Black Water and the Black Water Tactical
I have a problem with Sigs, well not really a problem...I shoot high thumbs and as a result the slide will never lock open on the last round for me and it bothers the hell out of me. I don't want to change the way I shoot just for one gun as I shoot ALL my guns with high thumbs. I do not have that issue with tehe CZ.
I took the pleasure of renting a SP-01 in 9mm a couple of weeks ago and I was impressed. The double action trgger seemed better than other Sigs I've tried. Currently all my autos are some form of single action and I have a hard time switching to traditional DA/SA guns, with a 226 I shoot low and left at first until I get used to the trigger, with the SP-01, I was just shooting low indicating that FOR ME the trigger was a little better.
Don't get hung up on the higher cap mags of the SP-01 and Sig BW-Tactical, if you carry the gun you're going to want a flush fitting mag (one of the reasons I like my XDM, 19rds in a flush fitting mag) and use the larger mags for reloads. There may be higher cap flush mags available, but who know if they work well.
The Sig has a better overall reputation, but the CZs aren't bad either but I give the nod to Sig for durability. With the Sig you can have the Short Reset Trigger installed which IMHO is THE BEST trigger system for a traditional DA/SA gun.
If you're looking for a carry gun, more hoslters will be available for the Sig, but there are plenty of holster makers that make holsters for the CZ, but EVERYBODY makes holsters for the 226.
Looking at the three guns, I see a couple small differences.
The CZ has rubberized grips, the original BW has wood, the BW Tac has the rubberized magwell grips. All three have night sights, but the original BW has a red front, and the BW Tac has the TFO front sight. The CZ doesn't have the greatest of cocking serrations and the rear sight is of a higher profile, I don't like that as it makes grasping the slide a little more difficlut and I catch my hand on the sight while doing clearance/failure drills. On the Sig I don't like the decocker/slide stop arrangement and prefer the more traditional locations of the CZ levers, but prefer the cocking serrations of the Sig.
You mentioned the weight of the CZ, it's about 6oz heavier than the Sigs, but that weight is all out front and makes the gun very controllable where muzzle climb is concerned, the Sig on the other hand has a higher bore axis and has more muzzle climb, or atleast that's how it seems to me.
Of the three, I would probably take the CZ and put the rest of the $$$ into ammo and holsters, simply because for me the gun feels better in my hand, I shoot it a bit better, and I prefer it's controls. yeah I have an issue with the cocking serrations, but I can work on that.
I guess you have to look at budget, availability, and what you want on the gun out of the box.
I forgot to add: The Sigs come with 4 or 5 extra mags pending on which model you purchase and the regular Black Water does come with an extra set of grips as well and the BW Tac all ready has the SRT (Short Reset Trigger)