33rpm vs 45rpm - which is better

in my experience, 45 sounds "airier" [cleaner extended trebles, greater sense of EASE from bottom to top esp. towards the inner grooves] than 33 but that it also has a slightly higher volume of surface noise, what noise there is in higher in pitch and more audible to me, the effect is similar to being outside in the wind and you hear the wind pick up. 

NOT a crap shoot.

Correctly engineered the 45 will always sound better because the higher speed enables more faithful recording of the music.  Compare with reel to reel tape - 7.5ips is better than 3.75 and professional studios often used 15ips.  Some of those recordings remain the best masters we have.

Consider - an LP should not contain more than around 20 mins music per side.  More than that requires compression of the grooves which reduces dynamic range (but look at the brilliant job Decca did on the Stones' 'Aftermath' that runs 52+ minutes) .  Do the maths - cutting less than about 9 minutes on a 45 side allows the engineer to cut at a higher level without crashing the grooves.  But if you try to cram more than that, then the advantage is gradually lost..

I bought a lot of used 45s in the 80s and 90s, mainly 70s and early 80s rock.  As others have posted, many of these are the best sounding vinyl I have.  A particular favorite is Frank Zappa's Stairway to Heaven b/w Ravel's Bolero - both outtrageous over-worked parodies of the originals.  I also have singles by most of the 80s big names.

@emrofsemanon    If some of your 45s are noisier, it is because they are dirtier, or perhaps they were played a lot or mishandled by a DJ in the day.

45 RPM

I’ve heard audiophile releases by the same company in both 45 and 33 versions and the 45 version is slightly better—more “open” sound.  But, in this particular instance, where the 45 version is also on a single disc, one has to wonder how that was accomplished and whether that entailed some other compromises.

45 LPs don't do it for me because normal sides are cut in half and usually better sounding LPs are originals, not recent remasters. I have a few but don't play them very often at all even if they may sound better, which is debatable.