I've been dealing with hyperemesis... I was first given Zofran (in the ER, and then as a prescription), but it was giving me HORRENDOUS constipation (and my nursing toddler loose stools, ironically), so I was switched to Phenergan, after a lengthy discussion with a pharmacist and the nurse at my OB's office. Technically, both are class C, I believe, which means that "not enough research" has been done to determine whether they are safe. However, if you google Phenergan, you'll be able to see some of the preliminary research that has been done, and it looks good.
From what I understand, Phenergan is a bit "older" than Zofran, more is known about it, etc.
Unfortunately, Phenergan doesn't seem to work for me (it actually seems to make my tummy feel worse?
: ). So I'm just going to take the Zofran when it seems like it's that or head to the ER. (I've pooped 3 days in a row for the first time in *weeks* and it feels great.
I agree that sometimes, you're really between a rock and a hard place with the barfing and there are no easy choices. I hope you're feeling better.