I've got a Levin.
Personally if it was the only 2 you have to choose from then i'd go the stivo.
however, i would hang out for the new one simply because its new and would be better in the long run to have a 'newer' model.
Having said that tho, depending on how far you wanna go with your mods, or no mods at all.
For torque mods, i'd go the levin.
Simply the car is easier to drive, wider torque and power band, although lower power, but the ratios and combination allows awesome cornering ability at close to peak power, would go even better with LSD, (harder to corner in lift (peak power) in a stivo, unless you're like shao ) and! its cheaper to boost and are Japanese built!! :)
For power mods, i'd go stivo.
With a mild mod, the stivo will quite happily sprint and kill a V8 down the straight, however, the peaky power takes getting used to and if you're not ready or prepared to rev the engine up to get moving then this is not really the car you're looking for. Awesome fun, but the reality is you can't really use lift everywhere. Spend your money on mods wisely on a 2zz, i'll be great fun, but without an LSD it'll loose out to the rivals of fast NA 4s in the category. Down the straight, you'll kill a levin by a good 1 to 2 seconds, but on stock, you'll have problems shaking a done up 1zz. :) ( and no chance to shaking or even pulling away from it on a uphill/downhill mountain run).
Other than that, levin seats are better than the stivo leather ones as it offers more support (again its a different in the conquest, and again different in the acent.)
My vote:
Bang for buck, Stivo. (with mild mods, $2k+)
Mods, 1zz. (given you have to a good $5k+)
Hope this helps. :)