Mega churches give me an icky feeling too. Probably because they remind me too much of a district convention. I would never go to one (I do belong to a church with about 300 members tho and love it). I invite people to church whenever it seems natural. It doesn't make a difference to me if they come or not.I treat them the same. I have as many atheist or agnostic, buddhist or muslim friends as Christian friends.
Maybe you are a bit paranoid cuz of your life experience. But there might be something behind it, especially if these same people kind of ignore you after you reject going to their church. Mega churches seem kind of both culty and impersonal at the same time. There's nothing whatsoever desirable about that for me.