I lived on and sailed a Ballad from the mid seventies to the early eighties. There were a couple of Vegas around. These are excellent boats, well made and designed for rough seas. I sailed a couple of times on the Vegas, and remembered it was very similar in behavior to our Ballad. If I remember correctly, the Vegas did exhibit a bit of weather helm (not much) but the Ballads were just about dead neutral on a close reach. The Ballad will point higher than a Vega, but the Vega is certainly no slouch upwind either. On winds greater than 15 knots is were these designs really shine, they are not 'light air' boats by any stretch. I remember we wouldn't start reefing main until around the 20 knot mark. Just about everyone else were dropping sails/reefing and we'd being full blast with a Genoa and full main. We LOVED the time before tropical storms would hit the gulf . . . great sailing weather! They are not roomy boats, but very much driven by IOR/MORC rules at the time. Here is a quick dis/advantage list as i see it
Support: Vega wins hands down. Many were built, and there are a number of support groups that you can find by googling. Not many Ballads were built, but there are some websites out there (mostly in Europe?) dedicated to the Ballad.
Rigging: For trailering Vega wins. Ballad is stepped to the keel, the Vega is stepped to a compression column. For strength, the Ballad. So I guess they are tied! The Ballad (our year, at least) has this weird boom roller reefing; it always worked flawlessly but I was suspicious of it in general. I've read some issues Vegas have had with their compression columns, but Ballads have had issues with the keel to mast attach points as well.
Looks: Ballad wins. I love the looks of both of them; But in my eye, the Ballad is drop dead gorgeous.
Auxiliary: Ballad Wins - We never had any major issues with our diesel auxiliary. If the battery went out, we could always start it with the crank and compression release. Folks have complained about reverse in these boats; but we could back straight out of our dock and go w/no problem. The Vegas I'm familiar with had gasoline engines - boo!
I'd like to see some boats that are more modern or manufactured today that are similar in seaworthiness and good looks.
Good luck in your search; I'd purchase the best of what I could find between the two.
Mark