Medusa or Astolfo?

I prefer Medusa, especially when she gets her 3rd skill. Astolfo sucks

I suggest Medusa. Astolfo is terrible for a 4-Star Rider. He could have been a decent tank like Marie if he had the fitting skill set but... unfortunately he has not.

Astolfo's only real advantages over Medusa is that he has a higher stat capacity (both grailed and not grailed) and that his Noble Phantasm applies Evade on him.

However, Medusa has a lower rarity, thus a lower cost and an easier to max out Noble Phantasm, the stat gap to Astolfo could be filled with some Craft Essence.

I personally would use Medusa if I didn't have Marie Antoinette already, but both look like Critical Star Generators rather than damage dealers or supporters. Sadly the Rider Class is not really fit for that role because they love to use what they produce themselves. Just use whoever you prefer I guess.

They're pretty much even in terms of gameplay performance in NA right now, with Astolfo having better stats, a slightly better NP and a more crit-friendly card spread, and Medusa having better versions of the same skills. However Medusa thoroughly outclasses him after Strengthening later.

If you just want an AoE Rider to counter Casters, either one will do the job just fine, but I'd forward that Teach can contribute just as well as either of them while also being cheaper to use and max, providing party bonuses and having an infinite duration Guts skill.

Unless you really like Astolfo, don't bother using him as he's very underwhelming for a 4 star.

With the sole exception of Boudica, every other Rider in NA offers more to the party than he does. He becomes slightly more useful once he gets his 3rd skill strengthening to charge his NP gauge since the 3 time dodge his NP grants is pretty useful, but it isn't enough to make him anything other than mediocre at best as his NP gain is still horrible.

Medusa, her attack buff is for 3 turns, her stun is better, and soon will have a 3rd skill wich charge np 20%-30% depend on level, and you can use her NP5 easiest.

The only reason ppl use Astolfo is because he is a trap without this will be like Fionn, hate for everyone and a inmediatly rare prism, terrible servant.

At the end you must choose what you like more, remember that.

Use Medusa for AoE as she's cheaper to level, has a powerful NP, and just rely on support Riders if you need more.
For ST, in a couple months you'll be getting Rider Kintoki as a welfare who's ridiculously good and never look back again.