i have opportunity to do this side trip in Myanmar. not sure which to do. thanks in advance

Neither one of these would be at the top of my list. Tell us where you plan to go in Myanmar, and we can be more helpful.

i am doing trip for 2 weeks in Myanmar. I am getting in 2 days early so was looking for something to do. Tour group suggested either of these locations as an add on. Any additional sites would be most welcome.

Where does the tour go?

Golden Rock was fabulous, not so much for the rock itself but because this is a pilgrimage site for believers. It was incredible to see the devotion and all of the believers who were camped out overnight at the site. However, if you decide to do this be sure to stay overnight up at the site itself. And, get a good guide who can explain all of this to you and help you with the transport to the site. Getting there is actually part of what makes this such an interesting experience.

I do not think Bago is particularly exciting but Golden Rock is nice. Hpa-An in Kayin State is also a nice add-on from Yangon. Enjoy!

As Bago is on the way from Yangon to Golden Rock you can take that in as well.
SS

If you leave 05:00 am from your Yangon Hotel, you can visit to Golden Rock first and then Bago.

We stopped at Bago for a coupl of hours on the way by car from Yangon to Bagan. The place would have been alright, but the constant pestering for money by youngsters was a big put-off.