Properties of a good steak?

I've come across two great, and very different, types of steak. The first is typical in Argentina and is not aged at all, but from a young calf (6-10 months old), free ranging and grass fed (hence not like classic veal). This is really juicy, tender, and with a very "bright" taste. Good high-end Argentine restaurants usually serve meat like this, and in the UK you can order it from pampasplains.com, which I think is great.

The second is from an older cow and dry aged to tenderize, but the aging also gives it a deeper, more bone marrow-like flavour. The best I've had of this type was a cow from Limousin in France, served in Paris at a small restaurant called Le Sèvero (8 rue des Plantes, 14th Arrondissment, reviewed in the NY Times a while ago). It was amazing! In London, 32 Great Queen St's "Hereford beef" is a similar style and also excellent. They get it from a Hereford farmer called Tom Jones (seriously), who serves several restaurants.

Good steak should never be marinated in anything - all it needs before cooking is salt, maybe pepper if you like (though I sometimes eat it with Coleman's English mustard).

I'm fairly sure that grass-only feed is important to good meat, i.e. no cereal-based fattening-up, though it's hard to separately test this one variable. Breed also clearly matters (all Argentine beef seems to be Aberdeen Angus or Hereford). I love a nicely marbled, fatty steak like the ribeye, but my (Argentine) wife prefers leaner cuts like sirloin and filet - clearly a matter of taste.

Jeffery Steingarten wrote a lot about this in his book The Man Who Ate Everything.

While there is a lot of "preference" here, there are some things that just make steaks better.

Dry aged beef, ideally 5 to 6 weeks intensifies the flavour, though it also reduces the amount of usable meat, which is why it's more expensive. Additionally, dry aging increases the "gaminess" of the taste. Wet aging provides some of the benefits without as much loss, but it isn't as effective.

The more marbled it is, the better it is. The flavour and moisture of the beef comes from the fat, so the more lines of fat through the raw meat the better the flavour and texture will be once it's cooked.

Thickness is going to depend a lot on personal preference. You can cook a thinner steak to a perfect medium rare or a thick steak to well done, depending on the temperature and style of the heat source.

Me, I like a thicker cut 36-day dry-aged sirloin steak, liberally salted and peppered served medium rare, with a slice of brie cheese on it.

A ribeye is my answer. You want to get a steak marbled well with fat, rather you eat the fat of not. That is where the flavor hides. My sister turned me on to Allegro liquid marinade, they have many different varieties to choose from.