Straight Futanari (SF), 2, I gave this a 2, because as I touched upon in the TG poll, I'm really more interested in the idea of futafication rather than futa in and of itself. That is, I'm not interested in just random dick girls you find in a lot of hentai. I'm really interested in a female growing a cock, usually as part of a forced transformation.
Realistic Penis (RP), 5, realistic is fine and unrealistic is fine as well. Cut or uncut (although cut seems to be the normative in most fiction and art). I've never really thought about the idea of self-impregnation with this. *lol*
Science Schmience (SS), 10, this is where it really is for me. Grow it huge, use mad science or evil magic to make it happen, practically give it a mind of its own. For a good idea of what I dig, umbrafox's Liam and Liam and Lorele sequence are where it's at!
Balls (B),7, love it when she grows a pair but it's not needed; and there needs to be no explanation as to why she can still cum (see Science Schmience)
Cum Factory (CF), 10, for me, this is what really touches on the futafication process. I like the idea that being futafied forces the woman to feel sexual arousal in the way a male does—a big and obvious physical sign of being horny where even a little physical stimulation can set her off. Cumming is a big part of that (no pun intended).
Ejaculation Size Small (ESS), 6, works for me.
Ejaculation Size Medium (ESM), 9, probably optimal
Ejaculation Size Large (ESL), 4, not opposed to this, but it can be a bit cartoony at this level.
Temporary Change (T), 5, like most answers to this question, don't mind if it ends up being temporary in the end, but I like the characters thinking it's gonna be permanent when it's first happening.
Burst Through Clothing (BC), 10, my favorite. The clothes ripping doesn't have to occur via futafication if it's destroyed by other parts of a transformation, but futa-destruction is welcome. I love the idea of splitting the front of her jeans as her growing and hardening dick expands or it gets so big it grows up underneath her blouse or sweater until it finally busts open the front of her top.
Mutant/Demon Cock (MDC), 9, this is great, especially if it's part of an over all transformation, such as into a herm-succubus or some eldritch abomination.
Multi Cock (MC), 9, this is also great in the right circumstance. I also enjoy other body parts TFed into dicks (e.g., GrymmBadger's Amongst The Ruins).
Always Fits (AF), 6, if it fits but really shouldn't, I just try not to think about it too much.
Size Category Small (SCS), 6, can dig it as long as it fits with the context of the story.
Size Category Medium (SCM), 10, this is probably optimal size for me.
Size Category Large (SCL), 6, can be cool if makes sense in context (e.g., turned into a large beast so needs a sizable cock to go along with the new form)