... I pick one and stick with it.
I've tried most thing to achieve the "ultimate level" and somehow each failed in someway or another. Electronic, digital, laser heck I almost tried nuclear (couldn't get the proper licensing). I looked at all the levels B&H offer and in the end decided that this was just a ploy to have me spend more money.
I thought I'd level the tripod before placing the camera on top then level the camera. Didn't make a heck of a lot of difference. I tried this on a level piece of course concrete; Tripod was level however as soon as I locked in the camera the camera showed it was off by just a hair. I thought about getting a surveying equipment thinking if it's good enough to set boundaries it should be good enough for me. Then I rethought the entire process.
Since going with the WRS I've seen a marked difference in how level my images are. Part of it is the tripod (it can double as a jack stand), part of it can be attributed to the Arca Cube (I stopped watching the levels). I only concern myself with the set of levels on the WRS. While I could use the IQ I haven't really felt the need. I also use my eyes.
What I've found for the most part is that a flat stitched image of 2 or more files consistently produce image that give me at least two sides that have 100% information while the other two have more than 95% and in the areas lacking I have less than 2 pixels of missing information. For me that's close enough to level.
Since relying on only one set of levels I've saved money and no longer have to answer pesky question of why I needed a nuclear use license.
Don
Written somewhat tongue in cheek to back up the wise suggestion given by Graham.