No contest between the two routes you suggested, IMHO, when it comes to scenery and overall ride satisfaction. Hope - Princeton is an amazing ride, both for the scenery and for the twisties. Princeton - Keremeos is also nice along the Similkameen River. Just watch for the wildlife. Keremeos to Penticton is also great, around Twin Lakes area especially. The only downside right now can be Penticton to Kelowna, as you have to try to avoid the road closures around Summerland. Check out
www.arthon.com to see the closure schedule.
(Further, if you like wineries, Penticton to Kelowna has that covered. If however, that's not a big deal to you, and you don't mind going even further out of the way, I'd go through Keremeos to Osoyoos, take Osoyoos to Rock Creek, then take Hwy 33 from Rock Creek to Kelowna. It's kind of the longer, back way into Kelowna, but beautiful. To compare them, Penticton to Kelowna on Hwy 97 follows the valley and lakes, while Osoyoos to Rock Creek to Kelowna on Hwy 33 is more mountainous and out of the way. Either way, you can't go wrong.)
The alternate you suggested, ie. Coquihalla Hwy to Merritt and Merritt to Kelowna, will be much faster, but it's boring for the most part. Just open freeway and not much to see.
Not sure what your ultimate destination is, ie. whether or not you plan on going past Kelowna. If so, I have heard that the route suggested by Calliway is gorgeous. It's definitely at the top of my list for this year.