Regular soda in the US tastes like crap compared to the real cane sugar versions that are sold in every other country. Just go to Costco (some other stores sell it too but Costco is the biggest I think), and buy the bottles of Coca Cola that are made in Mexico. You'll taste the difference immediately.
The reason I get diet coke when I eat out is because I know I'm already eating unhealthy, I don't need the extra calories from the soda. Hell a Big Mac has 550 calories by itself (no fries, no drink). A cup of regular soda has 300. The Big-Mac will fill me up, but the cup of soda won't hence it's just empty calories.
We still got the real sugar version of Mtn Dew (and some other soda's) here in the USA. it's just listed on the 'Throwback' version of Mtn Dew and yeah you can definitely notice the difference in taste. before i tried that myself a while ago i always assumed people where exaggerating the difference but anyone who regularly drinks Mtn Dew (and i imagine it will be the same with Coca-Cola to) will definitely notice the difference in taste between the 'high fructose corn syrup' (i.e. the regular common one) vs the actual sugar version(i.e. the Throwback one).
but with all of that said... even the regular high fructose corn syrup stuff we typically have here in USA still tastes good (easily better than diet soda) but i do prefer the actual sugar one IF i can find it. but the throwback version of Mtn Dew is more of a luxury thing here as i don't seem to find it in 2-liter bottles much as that's typically what i get in general. i most commonly find it in 20oz bottles and 12packs of 12oz cans.
but thanks for the info on Coca-Cola as i still have never had the real sugar version of that.
as far as the whole McDonalds thing... i would just eat there a bit less and when i do eat there i just would have the big mac/small fries/small drink.
p.s. but as you know... the reason they use the HFCS (high fructose corn syrup) is because it's cheaper to make then using real sugar.