Its complicated...you will end up with a genetic mix of the two peppers with all the dominate traits presenting (IE spicy is dominate over sweet, red over any other color, pod shape is complicated, but plant growth habit (bushy vs tree like, vs vegetable like...).
That said, its still likely to take after its momma as an F1... So if you have a bell pepper and lets say a Jalapeno that cross, pick the seeds from the bell momma and you';ll probably get: it will be spicy (though only half as hot as a jalapeno), some what larger than the Jalapeno, matures to red.
The other way would be mostly similar, though it would likely favor the Jalapeno in appearance more so than the bell.