all three of those choices are fine IMHO. they all do the same thing, they are both good brands. really cant go wrong with any of them. i am partial to cobb myself. as i dont have a lot of experience with grimspeed. but ive heard they're a good brand.
anything is better than your stock catted uppipe. thats got to go asap. esp if its been on for 98k miles. its a hell of a job so plan on an entire afternoon or possibly a whole day if your by yourself in your garage. but its worth knowing your turbo is safer, youll get about 10 hp out of it. and slightly quicker spool up.
pb blaster/wd40 is your friend. expect and prepare for some broken bolts and bleeding knuckles. if neither happens its been a good day, if both happens. its still been a good day and at least you were prepared for it