Is it better to travel to Buenos Aires with blue dollars or should I exchange before?

The best move is to change money directly in Argentina, but be strategic about where you do it. The blue dollar there is still better than the official rate, and while the legal risk is minimal for tourists, street changers aren't the safest option. Instead, you can use legal exchange houses that offer much better rates than official banks, especially in tourist areas like San Telmo or La Boca.

If you travel with a credit or debit card, honestly that's the most convenient. Many shops accept dollars directly too, though at a rate that doesn't work out great for you. What I'd definitely avoid is changing everything before you leave your country, because the rate difference is pretty significant and you'd just be throwing money away for nothing.

The strategy that works best is bring some cash dollars (just in case) but change most of it already in Buenos Aires at a registered exchange house. Check with your bank what options you have available, because some have agreements with entities there that offer decent rates. And yeah, keep an eye out for street changers even if they promise the best rates - it's not worth the hassle.