Ros - not keen. Certainly wouldn't use it as a standalone. Rosie, Rosa, Rose, Rosemary, Rosanna and Rosalie are all nice?
Anna - like it
Hannah - love it
Helen - not keen at all. Don't know any young ones. It seems dated to me.
Ada - quite like it
Olivia - like it
I'd go for Hannah by a long way. Second choice would be Anna, then Olivia.
Your names seem to fall into two 'camps' to my ears.
Classic but fairly modern still (Hannah, Anna, Olivia) and older, less used, kind of timeless but with a slightly more dated feel (Ros, Helen, Ada)
Other ideas of the first 'type':
Amy, Alice, Bryony, Charlotte, Catherine, Emma, Emily, Erin, Elizabeth, Grace, Georgia, Georgina, Holly, Isabel, Imogen, Jessica, Joanna, Julia, Katie, Lucy, Lydia, Miriam, Madeleine, Natalie, Natasha, Rebecca, Rachel, Sophie, Sophia, Sarah, Victoria, Vanessa, Zoe
And the second type:
Angela, Alison, Amber, Anika, Annie, Betty, Claire, Caroline, Deborah, Danielle, Erica, Fiona, Gloria, Hazel, Irene, Jennifer, Julie, Kimberly, Laura, Lisa, Melanie, Melissa, Michelle, Nicole, Nicola, Ruth, Samantha, Stephanie, Susan, Tiffany, Valerie, Wendy