IMO "more power is always better" but if you can't afford it, it doesn't really matter if it's "better." "Better" for me and "better" for you is not the same thing.
A lot of the answer depends on how you use it and how you travel. If you are spending most of your day driving (IOW, alternator running) then you can plug the fridge into the 12v outlet of the truck and not use the battery pack at all (or better yet, have the battery pack plugged into a 12v outlet to keep it charged up) and use the battery pack after you shut down the truck and camp for the night.
OTOH, if the way you camp is to drive to your destination, park beside the lake and sit there for 2 days without driving anywhere, then you might need more capacity from your battery pack.
BTW that is also a circumstance where an inexpensive 100W folding solar panel can help a lot. If it's sunny where you are and you're not going to be moving for a while, a 100w solar panel attached to your truck battery can keep it topped off even if the fridge is constantly running.
Keep in mind that long before these battery packs were invented, many people (including me) used to just plug the 12v fridge into our vehicle all the time. Yes, I did run the battery down enough to kill the battery a couple of times, but for the most part it worked fine (and in both of those cases, I was literally sitting, parked, for over 2 days without starting the truck.) Obviously in this case it makes sense to make sure your vehicle has the most powerful battery it can, and that the battery is in good health.
Other factors that will come into play are how cold you keep the fridge, what you keep in there (if you keep frozen stuff at the bottom, for example, it will stay colder longer without having to use as much power), how often you are opening it up (might be smart to get a plain cooler with ice for drinks, that way you're not opening the fridge every 15 minutes to get a drink) etc.
Don't focus on the TOOL (in this case, the battery pack), focus on the JOB YOU NEED TO DO. That is, you need to keep a fridge cold for X number of hours. A battery pack may do that. Or a 100W solar panel attached to the truck battery. Or a dual battery on the truck. Or just a new, high quality battery on the truck might be sufficient to do what you need done.