I'd stay away from ungrounded delta systems. That's old-school and prone to problems. Check out high resistance grounded wye. I'd elaborate, but my cell phone battery is almost dead. FWIW, it's "bus", not "buss".
Correct me if I'm wrong, but as I understand it, you're starting from scratch with a 3 phase 480 V 600 A system, and wondering if delta or wye would be better? I'll assume this is a machine shop with machine shop type loads... motors, lights, computers, etc.
First - the ungrounded delta system.
Ungrounded delta systems used to be popular in industrial facilities because it allows one leg of the delta to be grounded without causing a big explosion resulting in shutting the entire operation down. A monitoring system is employed to let maintenance personnel know when a phase goes to ground. This is usually accomplished by dim/bright lightbulbs and/or some type of annunciator. This is great if you're machine shop is churning out widgets (and consequently profit) at breakneck speed and a spindle motor or A/C compressor motor develops a short to ground. Since it's an ungrounded system, you can still run with one phase at ground potential without shutting the entire operation down. As soon as it's convenient, you can identify the location of the ground fault and repair or isolate it.
Now, the bad news.... Your voltage options are 480V, 480V, or 480V. Anything else will require transformers.
There's also a posibility of developing a pretty serious and equipment damaging overvoltage condition since the system isn't grounded. That's one of the reasons this system isn't used much anymore. It was discovered some time ago that under certain conditions (arcing ground faults if I recall correctly) the voltage can get very high with respect to ground - high enough to really screw up a lot of insulation on the system (motors, bus duct, power cable, etc).
Here's something else to consider..... Image a triangle (the delta) with a dot right in the middle of it. That dot represents ground, and the three points of the triange represent L1, L2, and L3. Take your finest ruler and measure the lenth of the three sides of the triangle. Each of those represents 480 units. If you measure from a corner to the dot you'll come up with 277 units. Because there's capacitance between the three phases and ground, the dot will remain somewhere in the middle (capacitive coupling).
With that said, if you meaure the voltage of an ungrounded 480V delta from phase to ground, it should be somewhere around 277 give or take. Now imagine the insulation in your motor windings, around your cables, and anywhere else there's insulation separating a phase conductor and ground. Under normal circumstances, that insulation will have to withstand somewhere around 277V.
Now lets ground a leg.... Remember the triangle and dot? Shift the triangle so one of the corners is on the dot. Now your phase to ground voltage just jumped up to 480V on two legs, and 0V on the other. This increased phase to ground voltage can stress insulation and cause equipment problems/failures.
The solidly grounded wye
This system is used a lot. It'll give you 480V phase to phase, and a solid 277V phase to ground. You'll obviously need a transformer for 120/240, or whatever other voltages you require, but that's no biggie.
One problem with this system is dealing with ground faults. Let's say West Unity hits 100 degrees and your roof top A/C compressor motor decides to crap out on you by developing a short to ground. Kaboooom... it's done... motor's shot and extensively damaged beyond repair... breaker's tripped... no more A/C and whatever else is on that circuit until you isolate or replace the motor and flip the breaker back on.
There's also a safety aspect of the solidy grounded wye to consider. Let's say you just hired Joe Blow, West Unity's finest and hardest working machinist apprentice. The kid's awesome... shows up to work on time, absorbs your teachings like a sponge, works his ass off. You don't want him to get blown up when he's too close to something the faults to ground.
Now on to the high resistance grounded wye
Same deal as the solidly grounded wye, but you put a resistor between the neutral and the ground.
A fault will follow the path of least resistance back to the source. In a solidly grounded wye system, if a ground fault occurs in a spindle motor, lots and lots of current will want to flow from that point back to the transformer neutral. This will mess up the motor pretty bad by letting the smoke out of it.
If you put a resistor between the transformer neutral and ground, you can limit that current to a safe value... say 5A instead of 5,000A. With some simple metering and control added to the mix you can monitor the current flowing through the resistor to tell you if a phase goes to ground. Just like the ungrounded delta, you can then pick a convenient time to track down the ground fault and fix it.
But wait... it gets better....
You can add a pulsing circuit to change the resistance value up and down. This will allow you to track down the location of the ground fault with a clamp-on ammeter so you don't have to shut breakers off one at a time to see when the ground goes away.
Anyway...
I think a high resistance grounded wye is ideal for a machine shop. It adds safety and reliablitly and doesn't cost much. It can also be added to an existing wye. SWMBO is wanting me to come to bed. gotta go. Thanks for hangin' in there 'till the end of this longwinded post. I tend to type a lot after just a couple beers.
... mmmmm .... well, about 24 yrs now. I like having things either 240 or 480. I have used transformers back and forth either way with seemingly no differance, but I guess if you are only pulling from the three legs, it's not much different eh?
