What would be some equivalents for this in Mexican/Argentine Spanish?
Oh man, that’s really cool.
Oh man, that sucks.
Maaaan, I’m jealous!
I can only think of “qué + adjective” and “dios” but I’m sure there’s plenty more.
Since you say that you can think of “qué + adjective” and “dios” as alternatives, I think that you don't really care to refer to a person but just express surprise.
¡Ay wey!,... [Most similar to "Oh, man"]
Chale, parece que va a llover. [Has a negative connotation. Slang]
¡Ay Dios!,... [Literal translation of "Oh, God"]
Híjole,... [Widely used]
No mames wey,... [Rather impolite but widely used]
No manches,... [A simmered down version of "no mames" that is not so impolite and is also widely used]
¡Ay cabrón!,... [Impolite rather harsh word, widely used]
Wow,... [Anglicism, widely used]
¿Qué pedo wey?,... [The litteral translation is "What fart dude?" It can be used to express surprise, usually with a negative connotation. It can also be used as a greeting.]
¡Ah, caráy¡,.../¡Caráy¡,.../¡Ah, que caráy¡,...
¡Carajo!,... [Has a negative connotation]
¡Me lleva el/la...¡, [Followed by a nonsensical noun or like: tostada, tren, chingada (swearing), carajo, la que me trajo. It has a negative connotation]
Caramba,... [not widely used]
"Ah, chinga,..." [quite impolite]
¡Ay, ay , ay!, [Not really used in Mexico but in the US. It is thought to be a Mexican expression, nevertheless I have never heard anyone use it in Mexico. It does appear in the lyrics of some Spanish songs and in the very well known "Ay, ay, ay, canta y no llores" Mexican song.]
It is heavily location-based. Probably every country has its own way of saying 'oh, man'. It depends in the country where you are basically. The answers above had provided with different expression so I'll just say that you have to be a little careful with those because, as I've said, depends deeply on the location.
If you use an expression from another country it will probably sound really off. I'm from Chile and we usually say 'oh, weón'. If we hear 'oh, tío' or 'órale wey' we probably gonna think you're mocking Spaniards or Mexicans (respectively).
Personally, I translate "man" in that context/usage as "tío"
- m. y f. coloq. U. como apelativo para designar a un amigo o compañero..
So I would translate your examples as
Tío, eso mola un montón
Tío, eso es una mierda/un fastidio
Tío, qué envidia!
You could use "jo tío" for emphasis if you wanted to (jo, jolín, and jolines are a sort of minced oaths in Spanish).
Of course "tío" has many equivalents. First that come to mind are "tronco" or "colega" (See ¿Cómo ha llegado “tronco” a ser sinónimo de tío / colega / amigo?).
I would not favor translating "Oh man" as anything with "dios". I would use it if the original included "Oh God" or "oh gosh" (or the like). Similarly, I would not use "qué + adjective" unless I was translating "so + adjective ("so annoying!", "so cool") or the like.
For an expression starting with "oh man" I would try to keep a similitude translating "man" as "tío".