Enjoy SPG - it's a great program. I think you'll find that while some benefits are better, some are worse.
I've been an SPG Plat for many years, and I have just as many frustrations w/ SPG as I do w/ Marriott. For example, getting upgraded to a suite w/ SPG properties is great. However, they are VERY inconsistent with how they do upgrades, from property to property. I
get very sick of arguing with them about these.
You mention the lounges being poor. That varies from property to property. If you think there isn't a large variety between property to property at SPG, you've got the wrong idea! They have a much larger variance - some are way nicer. Some are awful. I actually really like lounge access at Marriotts. It's better than "free breakfast" for me as I can go to the lounge whenever I want, grab a quick breakfast, bring it up to the room, etc. Also, if I have down time on a work day, I can work from the lounge and not feel stuck in my room. Most SPG properties don't have lounges, apart from Sheratons, and I don't really like Sheratons.
In any case, SPG is a great program. You'll enjoy it. I don't think it's leaps and bounds better than Marriott - it is worse in a few ways and better in a few. I'm fortunate enough to have been top tier status with both programs for some time now, and I'm pleased that the two somewhat offset each other. I love Marriott for the huge number of properties, the lounge access, the consistent experience I get, and the great credit card (signature visa). I use SPG because they have much nicer high end properties, cooler resorts in more interesting places, suite upgrades, and the flexibility of the SPG points program.