I would like to hear some pro and cons about these two Cassettes. From what I have read:
950 is slightly heavier
970 is nickle plated
Any other reasons for going to the 970 as apposed to the 950?

Oh yea, I am looking at the 9 speed versions

Is there any good reason for just going with the Shimano Ultegra 9 speed?

I've got two bikes with the 970, I've had excellent luck with them. Excellent shifting, excellent durability, etc. I suspect you'd get the same performance from the 950, but I remember something about the 950 looked noticeably crummy compared to the 970, I don't even remember exactly what it was. Regardless, I've spent the extra bucks on the 970's and haven't regretted it-

The PG-970 (12-23) is 230g and the Ultegra (12-23) 9-speed cassette weighs in at 203g according to Nashbar. I know this because I'm shopping, too. I'm probably going to get the PG-970 and save about $15. Besides, I like the nickel-plated version better.

Probably a good call, I think I will do the same. Now, where did you find the best prices?

According to weight weenies https://weightweenies.starbike.com/li...type=cassettes

Shimano Ultegra CS-6500 12-23 9-speed 196 g
SRAM PG-970 12-23 9-speed 189 g

They don't list a SRAM 12-23 PG 950, but for comparison, they do list

SRAM PG-950 12-26 9-speed 228 g
SRAM PG-970 12-26 9-speed 220 g

So my guess is that a PG-950 12-23 would be virtually the same wt. as the ultegra.

Shimano Ultegra CS-6500 12-25 9-speed 220 g and I prefer the 12-26.

I have the 12-26 PG-950. Really smooth shifting. I haven't ridden it long enough to find anything else out though.

Check out: https://www.bestwebbuys.com/bikes/index.cfm

Great site that searches out prices from various on-line dealers. Also, many dealers "price match".