I've been lucky enough to use both of these cards for a bit, and just want to give my thoughts on the cards, breaking down what they are good at and the differences between the two. Hopefully this is useful for some people who may be thinking of going for one of them. I won't really talk about PIM as I've not used him this year and he is quite obviously going to be incredible.
Overview of the card
So since the introduction in FIFA18, R9 is consistently viewed as the best striker in the game by the majority of the community. He is quite nimble for a big guy, has the strength and the size to go up against the best defenders, can shoot with both feet, 5* SM, Finesse and Chip Shot traits etc.
He is still the best striker in the game in my opinion, however I feel like the peak R9 was back in FIFA20, when he was quite clearly the best by a wide margin, you can see the evidence of this by literally every single pro using him during comps. Since then I think there have been some subtle changes that meant while he's still incredible, there's more of a contest now between him and TOTY CR7/TOTY Mbappe/PIM Puskas etc.
Things which R9 could abuse in previous versions are less effective this year, like Finesse Shot, dragbacks, shielding etc. Also the sticky dribbling that players like Neymar, Cruyff and R9 used to have in previous versions aren't as obvious this year.
His movement is still top tier however, he has the ability to sniff out loose balls inside the box and consistently able to get beyond the defenders with his power and speed. You will find that you can score a lot of tap-ins with R9, it might feel like he's not doing anything special but it becomes more obvious when you look at goal records over many games.
Things to keep in mind when using R9
In general, the main issue with any R9 cards is his workrate, the Medium attacking workrate means quite often when you are carrying the ball forward with your midfielders, R9 would kind of just stand around before making a late run. This isn't necessarily a bad thing as he could often find more space this way, but I believe this is the biggest problem for a player using R9 for the first time after they are used to strikers with High workrate. You need to hold the ball for longer with your ball carriers and wait for him to get into position, when he does start to move though he is unstoppable.
Another thing is R9 shouldn't be used as a dribbler, his dribbling isn't bad but it's not on the level of a Messi or Ben Yedder, so if you pass the ball to his feet when he's stationary, it just allows the defender to pounce on him. He does have 5*SM but he won't be able to pull them off as smoothly as a Neymar or Cruyff, so I would recommend unless there are ton of space, always look for through balls for him to run onto.
I also think R9 is much better as a lone striker as he will see more of the ball, in a two striker formation alongside a partner with High workrate he often just stays outside the box which isn't where you want him.
His stamina also isn't great, for a standard game he is usually pretty spent by the 70th min, you can mitigate this somewhat by giving him instructions like Stay Forward, Stay Central, Conservative tackling etc. But just be ready with an able replacement.
Difference between R94 and R96
So while R9 is R9, he is pretty much good at all the same things, there are some differences between the two cards and it's not as obvious that Prime is better than Mid.
The R96 is faster and a better dribbler, the R94 has more Strength, Composure and a better workrate (M/L vs. M/M). The workrate in particular means R94 tend to stay just a bit closer to goal where R96 would hang around further back, usually in between the half-way line and the penalty box.
One more thing that people don't usually look at but actually makes a notable difference is weight, R94 weighs 4kg more than R96, this makes R94 feel heavier when you trying to turn, even with an Engine on that gives him better Agility and Balance, however it also make him feel noticeably stronger as his model is bulkier.
Chemistry style also does make a difference for the two, R94 could use an Engine or Hawk, I tend to prefer Hawk as even with an Engine he isn't going to feel that nimble, while Hawk tend to boost what he's already good at. R96 has the advantage here as you don't really need to boost his Pace or Shooting, so you have the luxury of choosing beween Marksman, Finisher, Engine etc. My personal favourite is actually just Basic as it boost everything I want, although I've even seen people put Artist on him.
I think both of these cards are very fun and arguably the best strikers in the game, but overall I would recommend R94 just ahead of R96 due to value, there are enough small advantages of R94 that I don't think a 2m+ price differences are warranted. However if you prefer your striker to be more explosive and nimble then R96 is the obvious choice.
On the other hand, you don't go for R9 if you want value for coins, HM David and WW Alessandrini can't be beat on that front, but even from a nostalgic perspective R94 has that haircut so make that what you will lol.