<p>I prefer to stick with Canon L glass when possible, but as a hobbyist it is difficult to justify the cost of some of Canon's newest Mark II releases. Specifically the 24-70/2.8L, 70-200/2.8L and 100-400/4.5-5.6L upgrades. I have the 24-105/4L IS, 70-200/2.8L IS (Mk I), 70-200/4L IS and the 28-300/3.5-5.6L IS. When the Mk IIs came out for the 24-70/2.8L and the 100-400/4.5-5.6L, I decided to jump ship and go with Tamron's SP line. I bought the SP 24-70/2.8, which has image stabilization where Canon's Mk II does not. I also bought the Tamron SP 150-600/5-6.3. Both are just over half the price of the equivalent Canon lenses. While the IQ for the SP line may not be technically quite as good as the latest Canon L models, it is extremely close. And the build quality is right up there as well. I have not used any Sigma lenses lately, but from the reviews I have read, Sigma have also stepped up their game with their Art and Sport lines. I don't think there is as much distance between Canon and Tamron and Sigma as there used to be, except in price. And as a hobbyist, I find it really hard to justify the huge price difference for such relatively minor improvements in quality.</p>