I'm from Argentina, Buenos Aires specifically. If you have the time come here, the very urban feel of Argentina is at Buenos Aires and it has some lovely places. Palermo, Recoleta and Puerto Madero are full of pleasant, forested parks to enjoy the hot afternoons. San Telmo and La Boca, which are typical tourist staples, have the traditional landmarks as well as some nice eating places. just be careful with the heat, during the summer months it gets particularly hot and humid around the Pampa areas. The night life is diverse, long lasting, abundant and rather chaotic (with little to non-existent restrictions or enforcement on public drinking and something else here and there). Public transportation is not doing really well lately but for a tourist with no time schedules or work constraints it's ok: you could visit the Tigre municipal area and hop around the lovely little delta islands or even get a ferry to visit Colonia del Sacramento (as Genius already suggested), which is an hour away by boat.
Food is cheap for someone with strong currency (our local peso has been devaluing and we've gone through half a decade of high inflation now), you can get most things at a local almacén or supermarket, cooking it yourself or just buying a ready-to-eat lunch. Regarding what can you actually expect in terms of food I would consult Allie's blog (updated every week by an american ex-pat living in BA, in some bars there's a lot of them I mean A LOT):
http://pickupthefork.com/
Now safety: touristic areas in Mendoza, Patagonia or most of the Northwest region are rather safe, safer than most South American countries anyways, but you can still run into pickpockets or the occasional thief. As of now the "least safe" places in the country are located at the massive, mostly suburban and low-income areas, of: Cordoba City (in the Cuyo region), Buenos Aires southern neighborhoods (La Boca and San Telmo, both traditional and touristic, are close to some rather unpleasant areas that you want to avoid, like Constitución), the surrounding western and southern parts of the Metro area of the city have some dangerous places as well, but these are much more peripheral and you are not going to be there anyways. Rosario City is a different case altogether, it's one of the most beautiful cities around, located at the southern part of the Santa Fe Province and reportedly having some of the most beautiful women in the country (according to Rosarinos of course) it's an amicable city, nightlife there is good and the place lovely, but for some years now it has been dealing with a significantly strong drug problem, lots of drug related crimes, again this is mostly in the surrounding metro areas. Overall you are going to be fine, specially in smaller more traditional cities like the ones of the interior, Mendoza and the Andean region included.
Of course I'm missing a lot of info, if you have more questions of any nature regarding the country just post them.
PS: try to know your way around with some basic Spanish, the more educated urban dwellers manage English acceptably but we are far behind at the whole bilingual aspect, which is rather unfortunate.