In my experience, NOBODY has been able to beat genuine GM parts when it comes to roof rail/door/trunk seals. They're normally softer and obviously fit the best. As far as the best aftermarket, I can't tell you. I tried soffseal many moons ago and what a PITA. I swapped them out with NOS GM seals and never looked back. Maybe they're better now, but generally speaking, I've found aftermarkets firmer than the originals.
As for tips...
Some people don't use the recommended 3M black w/s adhesive, and if you don't, eventually the sh*t will pop out. All you need is about an 1/8" squiggle line of adhesive to attach. And get some wide popsicle sticks or better yet, those little wooden taste test spoons they use at grocery stores for those little taste test stations. Rounded corners. Works well for pushing the rubber into the channels.
Make SURE to use the push pins on the ends of the strip. If yours don't come with them, use GM p/n 8731909 or aftermarket equivalent.
I'm suspecting no T-tops, so I'd start with the C-pillar top corner and work my way to the front and then down the C-pillar. Test fit first to ensure you got the seal situated where you want it. Once you have it set in where the "final" fit goes, then pull out the C-channel (vertical) rubber to the top 90 degree corner, and apply adhesive (don't put too much on it) and attach the corner permanently. Then pick an end and work your way along the channel keeping the seal from being bunched up, but don't stretch it. Use finesse. Once at the end, put an adhesive strip along the middle of the strip.
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