If the Sun expect Chiney to be the star that her sister is, then they'll be disappointed. Chiney doesn't have the physical gifts or demeanor her sister has. Chiney will be a starter in the WNBA, but I doubt she ends up as first team All WNBA. If Ashja is not coming back, I'd probably draft Chiney over Sims but it would be a tough choice.
IMHO the Sun need a player who can create their own shots and take over the game during crunch time. I see Sims having the capability to do that more so then Chiney. I'm predicting Chiney wins some POY year awards and if Sun have first pick in the draft, it will be hard not to choose Chiney.