I see OEP and Select as being similar but different. Both are top notch blends. Select is really just a lean protein with high leucine content. It is probably the lowest calorie blend you will find with quality protein and no fat or carbs really.
OEP is also a top notch protein, with added MCTs, Fiber, and (thus) calories. For what you get, the calorie profile is good, but not as "tight" as Select.
I have tried a 55 serving can of Select C&C and loved it. It might be a little sweet for some, but I mix it in water most of the time and it was great flavor and texture-wise. I just got OEP Strawberry Cheesecake (my first try at OEP) and it is good, with a slightly similar texture and good flavor. Again, both of these are in water for me, and they taste really good...but even if they tasted bad I would probably still use them.
I'm cutting and I liked Select for this reason - it is low calorie/gram of protein. On the other hand, MCTs have a leaning effect and fiber can help make you feel more full on a strict diet. So both proteins can be used for the same goal - they just attack the problem from a slightly different angle.
Again, both are high quality products and I would use either.
For me, price has been the real factor over what I buy. I buy what's on sale. I got a ton of the VPX whey on sale a few months ago, and I'm finishing that up. I bought a tub of the Strawberry OEP for a change and then saw the Banana on sale for $15/can - so I bought 5 cans of that. Select is a little pricey, but if you get the 55 serving container under $50 it is only $10 more than 4 pounds of OEP ....so it's not a huge difference on the price.