I MUCH prefer the Jovani, but it depends on your personal style, colouring, and your shape. The second one is more classic and may get more repeat wear, and also may be more appropriate for your age and shape as the Jovani is quite "va va voom" vampy - I'm presuming you're young and skinny
and often the best thing if you're young and cute is to keep things simple and let your youth and fresh "glow" make the biggest statement of the outfit.
If you have large boobs for your size, I wouldn't recommend the second one so much, that kind of halterneck is not particularly flattering to the generously busty.
If you're less "endowed", that second one's a winner. Particularly if you have slender shoulders.
As others have suggested, the ideal thing would be to try it on.
If you do get the second one, team it with hair up and classic red lips and black "winged" eyeliner. Pick some really nice sparkly earrings and a glam sequinned clutch. If you really dress it up like this it will be very classic starlet and sophisticated.
If you get the beautiful, beautiful Jovani frock instead, do a subtley smoky eye and an ultraglossy lip, and have your hair loose and tousled or curled - you want body, but not too "done". Keep your accessories ultra-simple as the dress is already very fancy.
I loooooooove party dresses I do.