I have a few high watt mods. Here's my take on them:
iStick 100: Cheap. Both in price and quality. The chip is decent, but I find I have to crank up he watts a lil higher than what I run on other mods. The 510 connector is press-fit and isn't tight enough. Mod is 3 months old and my tanks wobble already. It's parallel, so you can safely use 20A batteries and get a TON more time between charges compared to other mods. But it will run on one battery, so you have to make sure both batts are installed securely. They can wiggle loose if you knock it around. All-in-all, it's a great mod if you want something small and affordable that won't make you cry if it breaks.
iPV4: My favorite. 125W, TC (though I don't use it), 8 hours heavy use on a pair of VTC4's at 80W, built well. Got it almost a year ago now and it has never given me a problem. Only complaint is that when it's brand new, the springs on the battery conections are SUPER stiff. I tore the wrapper on a set of batteries when removing them. Be careful when popping them out and it's more of a plus than a minus.
RX200: Just got it this week, so can't say a lot, but... Seems to be well built. Very small and comfortable to hold, but heavy. Odd shape makes it unfriendly for pocket carrying, but with a shorty atty like a derringer, I could hide it in the palm of my hand for a stealth vape. Slightly better battery life from the 3rd battery. I'm not a fan of TC so haven't checked that out yet, but in wattage mode it seems to work flawlessly up to 100W (that's as high as I've gone with it so far. Because of the shape, you could put a 30mm atty on it with only a mm or 2 overhang over the firing button.
I know several folks that have the Sigs you mentioned and they all say they are great mods. The only complaint I have heard about them is that they can't be upgraded.