Question : Problem: What is the best practice setup for 6 servers in a rack with one Smart UPS?

I have a rack with 6 Dell servers (PE 2850 and different models) and one APC Smart-UPS 3000. The rack has 1 power strip in the left side and it is plugged into the UPS at the bottom. Each server has redundant power and my question is....

Should I have both power cords for each server plugged directly into the rack power strip (that goes to the UPS)?

Or should I have one power cord going to a constant power (like one going into the wall)?

Do these servers run power active/passive or are they load balanced? If models matter let me know I can post them all up.

I really would like to know what the best practice is for a small setup like this. THANKS GUYS!!!!!!

Answer : Problem: What is the best practice setup for 6 servers in a rack with one Smart UPS?

This all depends on the level of power redundancy you are looking for.  First, I would check for the power requirements and make sure that everything seems to work out - you don't want to overload the PDU (Power Distribution Unit - the power strip) or the UPS or the circuit that this is all running on.  This may help a little with power requirements and lots of information like heat:

http://www.dell.com/html/us/products/rack_advisor/index.html?~lt=popup

Beyond that, each system is going to be different as far as active/passive goes.  Most Dell systems have only one redundant power supply.  If you have a total of three power supplies, for instance, two will be required and the third is the failover.  They are an N+1 configuration.  For all but the last one, they will be balanced but the redundant one is active/passive.  A 2850 has a total of two power supplies so only one will be drawing any significant power and the other is passive unless/until a failover occurs.  A 4600, however, is in a 3+1 configuration.  The system will hold 4 power supplies.  Three are required and will be drawing power and the last one is passive.

Back to the suggested setup.  Like I said, it depends on the level of redundancy you need.  The most robust I have seen worked like this:
Circuit 1 --> UPS 1 --> PDU 1 --> Power Supply 1
Circuit 2 --> UPS 2 --> PDU 2 --> Power Supply 2

This was set up for every system.  Each system occupied a one slot on each PDU and therefore had power redundancy at every level of the power chain.  Clearly, this is not a requirement.  Let's look at the situations you have outlined:
Case 1
Circuit 1 --> UPS 1 --> PDU 1 --> Power Supply 1
Circuit 1 --> UPS 1 --> PDU 1 --> Power Supply 2
In this case, your only redundancy is at the power supply level.  The circuit, UPS and PDU become a single point of failure.
Case 2
Circuit 1 --> UPS 1 --> PDU 1 --> Power Supply 1
Circuit 1 --> Power Supply 2
In this case, you have eliminated the UPS and the PDU as a single point of failure but the circuit supplying the servers and the UPS is still a single point of failure.  Also, you have reduced the level of protection from power events such as surges, sudden losses or storm damage.

I can't say what is "best" for you but these are some of the pros/cons of the cases you have asked about.  Also, we really don't know all the equipment/budget at your disposal to accomplish this.