Pro Vs Premium is a very serious consideration. You are likely (top of the market) looking at people offering out-of-production Pro's for as much as $8500.00.
Ten thousand gets you current production Premium.
The way the market is going, the value of what you buy will trend towards you looking back ten years from now and saying 'I can't believe I bought that so cheap in 2023!', so long-term, you likely will have a purchase that appreciates in value, no matter what you choose.
So the answer to your question depends upon some serious unknowns.
If you are looking at potential for flipping the pinball in a couple of years for profit, I would lean toward Iron Maiden.
I have a friend who is all about 'scarcity equals value'. If there are a TON of a particular machine made, it won't be as scarce. Foo Fighters - we'll have to see, but I suspect that due to the continuing demand for new product, there will be more Foo Fighters Pro version made than Iron Maiden.
So, if you are looking at profit, and you believe that 'scarcity equals value', you should get Iron Maiden.
If you are looking at 'what can I buy cheapest for the most value', then I might lean toward Foo Fighters. The best time to buy a pinball is when it's in production, dealers have lots of machines, and might cut you a special deal.
If you are looking at what most people would consider the best machine for fun, enjoyment, and potentially 'this is one of the best pinballs ever made in all of history', I'd lean toward Godzilla... with the caveat that Foo Fighters is a complete wild card, and might be the best pinball ever made. Who knows? But I'd lean toward Godzilla as a known quantity.
Back to the Premium/Pro discussion.
Pinball is very personal.
What is the best pinball FOR YOU? Well, it depends on what you like! So play them! Fall in love, and follow your very personal inclination. NO ONE can advise you on what you love.
I personally find that for most recent-production Stern pinballs, the PRO versions cut too deep. In an attempt to reach a price point they subtract and subtract and subtract, until most of the magic is gone.
Godzilla is an exception. My personal experience is that Godzilla PRO, while not as full and rich an experience as the Premium, is a quite fun game in the PRO version. It's a good playing game, and while being a quite different play experience, I find it quite fun.
Iron Maiden? I dunno. Haven't played enough of the Premiums/Pros to give an opinion other than "In general, with later model Stern pinballs you'd be better advised to get a Premium.' Furthermore, there may be one more production run of Premium Iron Maidens made, and that would be a good time to buy... when product is available. I don't think anyone is projecting another production run of Iron Maiden Pros.
Foo Fighters? Who knows? Nobody can advise you AT ALL yet.
Good luck with your purchase, and wherever you buy from, make sure you have a path to getting your machine fixed. It isn't going to be much fun if it's not working.