Are you planning to smoke 3 and IV 4? Then obviously 4.
Are you referring to the fact that heroin 4 is supposedly purer? Then obviously 4. "Supposedly" because 1) number 4 is (could be, rather, depending on where you live) cut with bullshit to the Point where X amount of 4 is just as good as X amount of 3, and 2) because you can't tell from the color of it what kind it really is.
(
If you do Everything correctly, I'd say 4 is much better as it's more effective (even if it's cut to 20 % one doesn't need acid to shoot it) and it's safer (like i said: if you do Everything correctly), as shooting something with a low level of adulterants, that's filtered away in your micron filter, in an amount that you know you can handle, is safer than either poisoning your lungs or shooting something too acidic (when sick enough, you'll use orange juice and a 100 unit*10-syringe, if thats what you have, just to....get well? (WhatS the transition from sick to healthy/well called in English?)).
And remember that, again I don't know how it works in NY, but in my part of the World, almost all heroin is Brown in color but it's not number 3.
If you're talking only about getting high (I assumed not since it's a HR-forum), and we're talking heroin 4 or 3 as they're defined, then 4 is much better.
But if it's about the same leve of purity and you intend to shoot it, quite a lot of people where I live report Brown heroin is more noddy and make you more "down" than White.I haven't noticed a difference.