When I worked in industry for a year we bought some silica gel from india that was horrible. It was incredible at grabbing your substrate and causing it to streak all over the place and hold stuff for a lot longer than was actually necessary. They only tested a small batch on a non-polar compound before buying a lot of 150kgs or so. Yeah its probably still sitting unused.
Whatman and silicycle are the two I have used. Silicycle has always been cheaper (both in industry and academia), particullarly with their TLC plates which ostensibly use the same silica gel (something that is nice when you can use the same on your plates and columns). In our combiflash we had ISCO columns (no telling where they got their silica gel) and some samples of silicycle columns and didn't notice any appreciable difference between those.
Yeah I would imagine though that most of the differences between brands is pretty minor. One might have more even distribution that will give slightly better seperations, but the way people run most of their columns is so inexact that I can scarcely imagine that it matters. It might matter in larger industrial scales where things are much more carefully controlled, but when we pack a column with 6 inches or so of silica gel, how much will those minor differences matter?
But yeah, if you are planning to switch, run a few columns on a variety of compounds with different polarities.