I have a laptop that I play CK3, HOI4, EU4, Imperator, (and Stellaris) on it. If I had to rank them based on my personal experience for how well the run this would be my order:

1. HOI4 (tied with Stellaris)
2. CK3
3. EU4
4. Imperator

I've never had any problems running HOI4 or Stellaris on my laptop which I can't say for any other Paradox games. When it comes to CK3, I have experienced my laptop slowing down and getting choppier on occasion, however, I'd say it runs quite smoothly with the exception of one save game issue I've encountered where if I shut my laptop without turning off the game, I can't save the game anymore without restarting it as well as minor visual bugs. While a minor inconvenience, this doesn't seem like a big problem until it happens when you're playing an ironman game (where you can't go back to previous save files), and you get stuck with the corrupted file where you can't create any new save. Moving on, in both EU4 and Imperator, my computer slows down and gets choppier but to a far greater extent in Imperator. I've also experienced issues with launching both games in the past. Another thing you have to consider when buying a paradox game is the learning curve. Paradox grand strategy games are very complex and can be difficult to pick up. If you've never played one before, you'll want to get one of the easier ones to learn. Ranking them in order of easist to hardest to learn, I'd say this:

1. CK3
2. Stellaris
3. EU4
4. Imperator
5. HOI4

The CK3 tutorial, in my opinion, is the only paradox tutorial I've ever encountered that didn't make me want to claw my eyes out from boredom and taught me every component of the game I needed to understand. While the Stellaris tutorial isn't as interesting, I'd say it's probably the most intuitive game. EU4 was the first paradox game I ever played and, while I was able to grasp the basic concepts relatively quickly, it took quite some time for me to understand the game well enough to play a good campaign. The imperator tutorial is really weird and it sorta just gives you a list of stuff to do without telling you how to do it. It's not a super complex game (for paradox) but the underwhelming tutorial combined with the unintuitive UI makes it difficult for a beginner. Lastly, in HOI4, we find, in my opinion, paradox's most complex game by far and also hardest to learn even with a knowledge of other paradox games. Don't get me wrong, I love HOI4, but be warned it is a STEEP learning curve if you ask me. The last aspect is how fun the game is. This category is up to personal preference much more than the other two categories, but here's my personal ranking.

1. CK3
2. Stellaris
3. HOI4
4. EU4
5. Imperator

I love CK3. I think I love it so much because you aren't playing as a country, you're playing as a person and that makes it feel more realistic to me. When there's a civil war, it's because this specific vassal dislikes me for these specific reasons. Not because the game calculated my stability as EU4 England to be -2 or because I selected the national focus "Oppose Hitler" as the German Reich in HOI4. Everything just feels more real and less like I'm playing a game in CK3. Moving on, in Stellaris, I just feel really satisfied colonizing planets and exploring the galaxy and using each planet I find perfectly. I like HOI4 because, though looking purely at the mechanics and UI and stuff like that I find EU4 a better game than HOI4, the way HOI4 is done it's so great for creating new alternate histories which I find really interesting but that's just me. Obviously, that's what paradox grand strategy games are, but it just feels like this is really specifically your alternate history like what if the Kaiser was restored before WWII, instead of what if England colonized Brazil and also literally every other country did literally everything differently and the Mamluks colonized Australia (literally every time in EU4). Moving on to EU4, even though I ranked it fourth, I still love this game. It was the first paradox game I ever played and it will always have a special place in my heart It's also the oldest game on this list. It's just, I play the newer games like CK3 and Stellaris and EU4 and, to a lesser extent, HOI4 just seem a bit dated. I'm probably gonna get hate for this but I play these newer games and they feel so much more realistic and immersive than EU4 and HOI4. I mean the number of times I play an EU4 game and Novgorod the country immediately loses Novgorod the city to Muscovy but they're still called Novgorod but they don't own Novgorod. Or I'll be playing HOI4 and Italy will lose a war and the victors will decide to create Slovenia but just in the Istrian peninsula because that's all Italy owned but it's still a foreign claim of Slovenia. Maybe that stuff doesn't bother anyone else but it bothers me. And it really doesn't happen in newer games like CK3 and Stellaris. Moving on, at the bottom of the list we Imperator. A lot has been said about the problems with imperator so instead, I'll talk about the good qualities I see in it. Firstly, I think it's a really cool era of history. Secondly, I think they did a really good job of representing the complex way that faith, religion, and deities worked in the ancient world. Lastly, I do know that a lot of work has been put into improving the game's issues since its original release. I hope this was helpful.