Overall I'd agree with Readonly and others that say the same, a well written slow is overall the best.
Well written slow burn > well written fast burn > poorly written fast burn > poorly written slow burn. When a slow burn is good there's nothing better, when its bad its pretty useless.
However, RedOwl has a good point, if the story fits it can make it better.
Either works as long as the story fits. There are some slow burn games with a story that pulls me in to the point I forget they're porn games. Like a lot of others have said, there has to be something there to keep me coming back.
To give at least two decent examples of a slow burn and a fast burn.
Slow Burn
I'd recommend
Sweet Affection by Naughty Attic Gaming is still ongoing and it does take a bit to get any involved lewd content, most of the beginning is mainly soft core. However, I feel it does build up the characters well and makes them feel more like individuals than just someone who worships your member. There are some Side LI that move a bit faster as well.
There is a bit of grind to this as it is sandbox style, but most events with the main LI are strict when it can happen so you can easily skip time to jump to the events and avoid repeating the same ones. The Dev also implemented a Diary system for the main LI which are some of the best part for building the characters as well I feel as it basically is how you get some insight to how they feel at the different stages of corruption essentially.
Fast Burn
I'd recommend
You must be registered to see links
it is almost complete, I think there is only going to be one more update based on the last update the Dev noted. This one does have very little story and gets into various scenes quickly.
This one is also sandbox but has almost no grind, there are various events for each time of day esentially and different levels of corruption but this one lets you downgrade/upgrade the levels to which ever event you want again overall. This way if you think a missionary at level 2 is more erotic than at level 3 you can downgrade to see it again. This one stands out as it has some really good models and animations.