If you're not into temp limiting, the Sig boxes have proven bulletproof for me - I'd go with the 150 if I had the choice today just because the price difference between that and the 100+ is negligible (I have a v1 Sig 100 that's been working great for 7+ months). I've heard good and bad (mostly good) things about the IPV4 as well, another comparable mod.
I tried the iStick 50, found the buttons rattly and inconsistent, the threading at the 510 connection subpar, and that build quality in general was just less than what I was expecting - but there have been lots of reports on "good" and "bad" batches of the mod, if you love yours maybe you got a "good" version.
So count me as a Sig fanboy who'd consider an IPV in this situation as well...one thing is that the temp limiting mods are about to do another round of releases, which ought to decimate the value of the straight-wattage market. So if you're not into TC, there should be (actually, there already are) some good deals out on last-gen tech. I'd be all over a Sig 150 like stink on a pair of week-old underwear, but my 100 still works great and I try to buy semi-new tech when I eventually do buy so I can relate to what the cool kids these days are vaping on...good luck whatever route you go!