Lens Advice for Spotting at Chicago O'Hare (ORD)?

Hey folks, I'm looking to upgrade my lens for some spotting at Chicago O'Hare (ORD) and could use some advice. I'm torn between the Canon EF 100-400mm f/4.5-5.6L IS II USM and the Sigma 150-600mm f/5-6.3 DG OS HSM.

I've been using a Canon 70-300mm which has been alright, but I feel like I'm missing those crisp long shots when planes are taxiing or on the runway. ORD is massive, and sometimes you're just so far away from the action. I want something versatile for different lighting conditions too, since ORD can be pretty unpredictable weather-wise.

Anyone have experience with these lenses, or have other recommendations? How do they handle in lower light situations or when dealing with the heat haze we sometimes get? Thanks in advance!

I'd go with the Canon 100-400mm. It's a solid performer and great for versatility. The image stabilization is top-notch, so it helps in lower light, and it's not too heavy to lug around. The Sigma 150-600mm gives you more reach, but at ORD, heat haze can be brutal, and more zoom isn't always better. I had a Sigma for a while, but ended up preferring the Canon for its reliability and sharpness. How often do you shoot in low light? That might tip the scales.

I'd say go for the Sigma 150-600mm if you're looking for those long shots. It's got that extra reach which can be super handy at a big airport like ORD. I used it once at a different airport and found it did pretty well with heat haze, but lower light can be a bit tricky. You might need a tripod or monopod though, 'cause it's a bit heavy. Have you thought about renting one to test it out first?