I'd go with whatever you feel best in: big cruiser or big sci ship. Honestly though, and in my opinion, if you are really torn, and can only buy one. I'd wait until we know more about the Vesta. Then you can better make up your mind.
However, I would wait until some more specs are available on the Vesta. So far as I know they should be out in a few days. According to the Tribble sub-forums, they've already got some beta testers on Tribble using them - you might get some preliminary and very subject-to-change stats on them.
Vesta has a shot of being a super ship with its heavy cannon mounting. Also if I had to guess I'd say its probably gonna get a 3 pack just like the Odysseys.
But the Odyssey is a super cruiser, It can tank, support heal, or run a mean tac heavy single cannon build.
So basically wait a week or two to hear the Vesta's stats and then see how well it can make use of those heavy cannons. Look for a base turn rate of 9 or better for a really good fit for them and the ability to run cannon skills back to back while not needed would make it a far better ship. So if the vesta shows up with a turn rate of 11 and a ltcmd tac I'd get it over the Odyssey. Other than that its gonna be a choice between which one follows your playstyle better.