I like actually sucking it before it gets hard and feel it growing in my mouth
Of my two boyfriends/partners, the first one (my ex) used to get super sensitive after he came so didn't like me sucking or touching his dick after he came, so I used to try and get him while he was soft. This was usually easy as he didn't get hard from only kissing or body contact.
The second one (my current) gets hard pretty quickly when we start getting... intimate

so that doesn't give me the opportunity to feel him grow in my mouth, he's also not a grower (he's a show-er lol) and even after he cums, he stays hard if he's still into it / horny, and can come again a short while later (multiple times, as I've learned haha) so never quite gets soft after cumming.