Welcome! I have jeans in a variety of cuts, styles and sizes, and I've made a name for myself on the forums as being especially handy with sizing and body types, so I think I can help :)
Check out this body type guide by the original What Not to Wear girls:
I'd bet good money you're either a Skittle (a pear without the butt, basically. For some reason I see this type in almost every Eastern European, like my mom, or East Asian girl. No idea why. I also have no idea why they call bowling pins Skittles over there!) or a Brick (athletic type with muscular legs but no hips). Both are super common body types, and I've had plenty of experience picking out jeans for both (bricks are a little harder to fit because you also need a bigger waist, and you're more likely to get the butt sag in a pair that fits both the waist and thighs, but I digress)
Here are superthreads in which I link the various pairs that will fit each size (regardless of what the tags say; I go by measurements)
I'd definitely recommend the Hillhursts, since the flap pockets will fill out your booty (and Paige runs smaller in the hips, but the wide leg cut will fit your thighs). The Jackies may also work if the thigh measurement works for you, since they're a bit of a wider leg and the clean back will fill you out a bit. For dress pants, I'd go for the Robert Rodriguez ones.
Out of all these, I'd most recommend the Paige Melrose. They're really stretchy and fit over my quite large thighs (if you're still on the figure guide, I'm the classic pear, so I have junk in the trunk and thunder thighs), so they'll be fine on you if you wear a 30 or lean towards a 31. They run smaller mostly in the hips so you shouldn't get the sagginess as much with these.
If you like skinnies (if you're a Brick, you'll look really good in them--they give you hips. Skittles, not so much), go for the Roxannes or, if you're really edgy, the Gwens...both are very stretchy. The skirt might also look really nice on you, especially if you're a Brick and need more waist room.
Hope this helps--welcome to DB! :)