Well, both have their own pros and cons. I have both to ease my life.

Honestly, most of my online purchases are charged to VOX rather than CIMB CR.
This is my own summary for these cards:
i) CIMB CR is a free for life card while UOB VOX is not, you will need to spend at least once per month (no minimum amount) to avoid RM 6.00 monthly charges.
ii) CIMB CR has no minimum amount for online transactions in order to be eligible for cash back but VOX requires you to spend at least RM 50 per transaction to be eligible for cash back.
iii) CIMB CR's maximum cash back for online transactions is only RM 30 (that means max spending for online transactions is RM 600) while VOX can be fully maximized at RM 50 (for RM 1k of spending).
iv) CIMB CR's has a fixed date of cash back crediting while UOB VOX sucks here and according to T&C, it is by 30th of the following month. Sometimes the VOX's system behaves while sometimes it doesn't. I'm involving BNM in this matter.
v) CIMB CR has cross borders charges (read
here) while VOX doesn't have.
vi) CIMB CR's maximum cash back for online transactions is only 5% while UOB VOX is 5.3% (5% - online transactions + 0.3% retail transactions).
vii) CIMB CR doesn't give cash back for flight tickets while UOB VOX gives.
vii) CIMB CR doesn't give cash back for UOBPayOnline transactions while UOB gives (refer to first post of
this thread).
So in conclusion, apply for both.

actually uob vox started out not that popular among us, as it exclude utilities payment too. but somehow someone started testing to pay via uobpayonline and later few more tested different utilities there, and then the rest becomes history. otherwise, uob vox will not be that good already if utilities are excluded.
i just used my vox for online purchase like lazada/11street/etc previously. but i will start to use it for bills via uobpayonline soon, now that many confirmed receiving cb from vox for utilities, and watami is dead.