Hello, I'm gonna try to answer this one, and I'll let JB cover anything I leave unsaid.
The 5-piece neck is a bit more tedious to assemble than one- or two- piece necks. Because of the added strength of the woods chosen and the gluing process, however, the energy from the strings is better carried to the top, giving optimum articulation, sustain, and volume.
I own a Legacy Premier model, and it is incredible. I could say that about almost every Avalon there is, I'm sure, but I would be safe to say that whatever you choose to invest in your Avalon will be given back to you, pressed down, shaken together, and overflowing!
If you're a fingerstyle player, especially one who uses alternate tunings and like the tone of a Cedar-ish guitar, I would check out the A325C Redwood on the Available stock page. I had the joy of playing it and I will never forget it. Blessings to you all!