I just got a quote from an installer for 2 options to connect to 2 Xantrex GT 3.0, which would be the better choice to go with:

1. 42 bp sx-170b which produces 5.98kW system
2. 38 sharp nt-s5e1u 185 which produces 5.86kW system

The price difference between 1&2 is about $4k.
So, would it be worth it to go with the BP panels, or would the Sharp panels
be a better choice? Is quality an issue between the 2?

BP panels are thicker cells and have 3 decades of proven performance, not this model in particular but BP in general

The comments on NAW about "not buying from and Oil Company" IMHO is silly, it takes HUGE capital investments to make PV panels, thats why names like GE , Sanyo, Sharp , Kyocera, BP and until a few months ago Shell are the Major players

For my $$, It would be BP first, then Sharp, either will be a really sweet system!

But that's $4k for a gain of .12kW... that's my concern, is it really worth the money, quality wise, to get BP for this high difference in cost regarding the panels?

I noticed that the Sharp is also mono crystal comparing to multi crystal for the BP. Any gain regarding single vs multi crystal?

I ran both panels thru the Xantrex String sizing tool, I don't know if you realize it but both system have panels that will make one inverter have 2 more panels. What would be nice is to either increase ( or decrease ) the panel totals by 2 panels, then you have identical systems.

Having identical system is a really good way to know if there are panel issues as the inverters will be close in power generation. Its a really good long term and FREE way to keep an eye on your system, having different array sizes means different operational points for the inverters so comparison is much harder

The sharps are nice spec wise panels, mono is good and the BP panels I was surprised to see are +/- 10% on the power rating ... pretty big gap.

The only thought I can say about the sharps is I would have a concern for as sharp cuts the wafers thinner than any other PV manufacture. So the potentional for crack cells could be greater than a fatter wafer. This is why the Sharps don't honor there warranty for RV or Marine enviroments

Having said this, if there less, than I would make it 40 sharps and have 2 identical systems. You still save money and you will know from day one if there are panel issues if the two AC outputs are off by more than 50 watts and or the mppt tracking is off more than 5 volts, both would indicate there is a panel in the string that is not upto par