Almost certainly all of the above, with religion likely the biggest factor. Say and believe what you like about the man; his historical legacy and pivotal importance (good and/or bad) is indisputable.
I think you're on the right track here. Unlike many other religions promoted on or alluded to on ancient coins, Christianity is still practiced today and Constantine (rightly or wrongly) gets a lot of credit for that. Because of that, his deeds come under more scrutiny today and are probably viewed with a different lens.
I have this little question on my webpage- “without Constantine would Christianity have flourished?” http://www.constantinethegreatcoins.com/
Does a coin of the vile man's son count if it was minted during the vile man's lifetime? These two coins of Constantine II were minted while Constantine I was still alive and well. Am I the only one here who disliked this emperor? At least I seem to be today. Look, I obviously don't hate him. As someone else mentioned, hard to hate someone who lived 1,700 years ago. I just don't like him, that's all.
That's one of my favorite types also. my page on these- http://www.constantinethegreatcoins.com//DAFNE/ when I actively collected them, I tried to get examples from each workshop- http://www.constantinethegreatcoins.com/dafgal/
I have mixed feelings about Constantine. Let's see - he boiled his wife, killed his son, killed his nephew, dismantled the tetrarchy, and also had Licinius executed. On the other hand he recognized that the seat of the empire should be in the east and selected a very strategic point. He ruled for a very long time and perhaps according to the realpolitik of the era, his actions weren't totally unusual, unseemly as they seem to us 1700 years later. I'll post a couple of coins later today...
I am in no way a fan of Constantine. RI Constantine I Folles 306-337 CE Captives VOTA Banner RI Helena mother Constantine AE Follis Securitas Nicomedia mint 325-326 CE 19mm 3.3g RIC-95 Sear 16619 RI Fausta 325-326 CE AE3 Spes stdg 2 infants SMHA 20mm 3.48g scratch over eye damnatio memoriae by Constantine
..all i can say about him is... he moved the capital....and named it after himself..and i gotta find my Fausta coin! Constantine "AD"
It may surprise you folks to learn that I actually like Constantine's mother a lot. She was an amazing woman. Helena, Mother of Constantine, 327 - 328 AD AE Follis, Antioch Mint, 20mm, 2.88 grams Obverse: FL HELENA AVGVSTA, Diademed and mantled bust of Helena right. Reverse: SECVRITAS REIPVBLICAE, Securitas standing left holding branch and raising robe with right hand, DE in right field, SMANT in exergue RIC80
Maybe my favorite Constantine series to collect. Constantine as the "eternal prince" with horseman leaping over enemy on shield. Below is an example with two fallen enemies. I have several pages of these, if any is interested- http://www.constantinethegreatcoins.com/sis/