Re: Preamp/poweramp vs. head
I like rack gear for flexibility.
It takes longer to configure and program, but is faster to setup and teardown once configured correctly. With a well setup rack you can connect a few cables and your ready to go.
Another nice thing is that your gear is protected by the rack. Less chance of beer damage or damage from flying bottles and such. Also, all your settings are protected, as the knobs aren't exposed during load in and unloading.
Another plus is rack amps are generally stereo. Good if your into stereo effects like chorus or delay. Along the same lines are stereo line outs. Handy for going direct to board if you don't want/can't mic.
On the other side, if your rig is simple heads can be easier to manage. All you need to do is connect your guitar/pedalboard/amp/cab and your ready to go. Things can quickly become more complicated if you have parts of your pedalboard in your effects loop. There's alot more line loss in a setup like that, as you can easily add 20' or more of cabling to go between your loop and your pedal board.
Lastly, racks are self contained, heads aren't. If you're running a power conditioner, attenuator, a bunch of stompboxes and a rack effects unit into a head, you'll have sh*t dangling all over the place and cables everywhere. If it's all in a rack, it's all contained in a rack. You walk in, plug in, and play.
Lastly lastly, you can get all the benifits of rack mounting stuff with a head, just mount the head inside the rack, or stack it on top when you set up. Plenty of people do it that way, and it works great.