Alphafly. Seriously. Not for all your training, save it for the hardest days and possibly the longest days. You will likely need 2 pairs - one reserved really for race day and near-race day training, and the other for the rest of the year selected training. You will probably benefit from another more durable training shoe to soak up the rest of the miles, as the biggest weakness aside from the Alphafly’s price is that it has been reported to lose its advantageous pop at some point, well under 150 miles of use by most anecdotal users.
The alphafly is the most cushioned of the carbon shoes I’ve used. It makes the carbon Endorphin pro seem hard and nonbouncy in comparison. There is a reason why big-mile marathoners love even training in it - the cushion and bounce really do allow your legs to go faster for less effort, and thus let them recover faster.
The big cush training shoes such as Hoka Bondi, Bondi X, Nike Invicible, Saucony Triumph, Brooks Glycerin - I’ve run in them all, often several iterations. They’re all good, they all have ample padding, and unfortunately they are all heavy and will suck the rebound energy right out of your step, meaning they really make terrible race shoes. On average, 20sec/slower per mile for me compared to carbon racing shoes, possibly more. I literally go up 2 entire classes of running ability when I go from these shoes to the Alphafly, even my Garmin VO2max meter gets super confused by my overperformance on race day with Alphaflys.
Of all the cush bouncy ‘recovery’ shoes, the Nike Invincible is the bounciest. Bondi and Glycerin are less bouncy (Bondi is weirdly firm, actually), and the Triumph is decidedly on the firm side. I have found by accidental trial and error though that the firmer the shoe for me, the faster it goes. The Saucony Triumph is def the most firmest and least bouncy of these cush shoes, but easily the fastest on my long runs compared to the others. Nike Invincible and Bondi are the slowest. It’s enough of a difference that I was wondering why I was able to run so much faster on certain long days than others, and then saw I was always doing it in the Triumphs. (Which still doesn’t touch the Alphafly or Endorphin pro).
Super cush shoes like the Invincible also should come with another warning - if you’re used to all that cush, it does make it harder to run in fast lower-cushion race shoes, and in fact, definitely increases risks of getting a calf or Achilles strain on race day if you intend to change it up to a race shoe. (I got a really bad one in my last race from exactly this - and before this I literally never have had a calf strain from racing, ever, in my prior 20+ years of running.)
I’ve mentioned it a lot before but I have longstanding ankle arthritis, so I can’t just go hog wild with low cushion shoes. I think my ankles are actually a great measure of midsoles - if it’s not as cushioned, I’ll start feeling the sharp pains at around the 20-30 mpw mark (and by then it’s too late as the bone bruising has settled in!) I’d love to run in Alphaflys all the time, but my ankles necessitate that I save the fast shoes for my speed sessions and only a few longer runs before race day.