Traditionally, it is up to the groom to select an engagement ring to be given during the proposal however there is usually heavy involvement of the soon to be bride. When it comes to choosing wedding bands, the waters have always been a little murky.
If a bride buys the groom's wedding band, traditionally, she will pick out the ring and vice versa. Nowadays, this is rarely the case. It has become more common for a bride and groom to choose their rings or pick them out together.
A bride may have her eyes on a matching set in hopes that her wedding band will complement her engagement ring. For this scenario, it is probably best that she go ahead and chooses her own.
On the other hand, the groom may not normally wear jewelry and might need help choosing a wedding ring that best suits him. In this case, the bride may need to help choose a ring that matches his style and that he will also enjoy.
It can also be challenging to choose men's ring sizes correctly. It may be wise to have the groom involved when choosing the ring to have it properly sized. This way, you'll be guaranteed the ring will fit on the big day.