Are you going to play the horn?
Or are you just looking put it on display and blow it occasionally?
If you're going to practice and play every day, in what setting?
Will you be playing in a variety of settings?
Do you have a reaaly good tech?
Do you have really deep pockets?
All the suggestions you've been given, are valid. Like many other members here, I regularly play an assortment of the horns listed above. I play an Aristocrat in the Big Band. My New Wonder, or "Chu Berry," as it's often mistakenly referred to, is my everyday practice horn. I've played and spent time with Martin altos too.
A lot of folks would use the Aristocrat as the practice horn and play the Conn in the Big Band. It's not a cut and dried thing, and that's my point. The best value for the money horn, for you, is going to depend on what you want the horn to do.
For example, the New Wonder has a BIG sound and it'd make a great lead alto....for someone other than me. The ergos of the left hand pinky keys, don't suit my long fingers. Also, for me, I'm TOO LOUD on the Conn and I have to work harder on intonation.
The Buescher, for me, is just an easier horn to do the job with. When I'm trying to play in tune and blend with the other altos, the Buescher does it easier for me. When I'm trying to execute my parts on uptempo Big Band charts, whilst coping with the fact that all the other altos are good sight readers and I'm the only "****e reader," the Buescher ergos are easier, for me. When I'm at home, working on refining my fingering and intonation, the Conn makes me concentrate harder and shows up all my bad habits more.
You're experience is going to be different to mine and everyone else's. My advice is to know what you want the horn to do, before you spend the money. They're all good horns. I'd go for a New Wonder, or True Tone, but only because you'll be able to get into one, live with it for a while, and if the marriage doesn't work out, get a divorce, without losing too much money. This way you'll have sufficent funds left to try one of the others. Just remember that the rarer and more expensive you go, the harder it is to divorce the horn, without losing time, money, or both.
The most important thing IMO is to really do your homework on the true condition of any prospective purchase. "Needs a few minor adjustments," is seller speak for "budget at least $1000 for a complete overhaul." Don't get burned. If it sounds too good to be true, it probably is. True Tones and New Wonders are so common that no seller is going to spend big money on getting the horn fully serviced before selling. You'd spend more than you're gonna get for it. For the buyer, it means that, there's a lot of good horns to be had, but you're very rarely going to get a $500 vintage horn that is in great condition and plays like a dream without any additional on road costs. Don't chase the bargain of a lifetime. It's too much of a crap shoot. Pay what the market demands for a good example of your chosen horn and then get it serviced.You'll be happier in the long run.
Hope all this helps.
The best bang for the buck? You aren't going to know