Why I support Paradox? Because I know that they support their games for the long term. The game might not be the best 4X at the moment (although in my opinion it does come close), but I know that a few years down the road Paradox will still be updating the game and creating new content. That in my opinion is something that more studios should take as a model, instead of launching a title and forgetting it in a year.
Yeah, the warfare could be a lot better, and the AI, and I would love a lot more specialization in for example tech, but I know that these are things that will get fixed in some future patch or DLC. I haven't yet seen a single game that came out of development in a perfect and best possible state, and the likes of Civilization 5 became great in my opinion after a few iterations and DLC, to the point that I'm not sure whether civ 6 is better than the comlete civ 5, but that will also change as dlc come out.
As for crippling bugs, I haven't yet ran into any of those. The latest AI not declaring war could have been one, but then again I started a game when 1.6.0 came out, and next day at work noticed that the bug had been noted on these forums, that day I didn't have time to play, and the day after that that I did play, the beta was already out. Because I hadn't met with any other civilization before I upgraded to the beta, I can't say that the bug really stopped me from enjoying the game.
And all in all, I've greatly enjoyed the game as it has been from the beginning. It could be better, and I wouldn't go back to playing the release version for anything, I think the changes have been for the better.
And really, it's not like any other studio is really any better. I just bought the latest DLC for Galactic Civilizations 3 and tested that out, but decided to stop playing it when I noticed that they've basically broken some of the original races by not updating them to the new system (I'm looking at you Yor, not getting anything extra from that cybernetic trait) and have such obvious bugs as for example plus movement speed bonuses only ever affecting those ships you have in space when the bonus is gained, and not any you build afterwards. Or destroying survey ships still taking administrators even though the ship is permanently lost. Also GalCiv 2 had this nice "feature" that even though you could easily boost your traderoute number to double digits, the maximum amount of traderoutes was fixed at seven or eight, so you could create a custom race that on the first day exceeded that number, and thus all of their technology that would increase the number did absolutely nothing. And even though this was reported, the devs just said "Meh, it is known that the maximum amount of traderoutes is 7".
At least for Paradox I know that they react to bug reports and start fixing things. I not right now, then at least in the future.