After much analysis, I have a very different player comparison for Breanna Stewart. See below (and I apologize for the length, but you know how lawyers love to talk).
1) Elena Delle Donne is a guard/forward. She is a 6-5 version of Katie Smith.
Breanna Stewart, on the other hand, is not someone to whom I would compare Delle Donne. They are tall, white, Northeast players with range. I think the similarities end there.
2) Candace Parker is a fluid, 6-4 post player. She can shoot within 10-12 feet with either hand (amazingly impressive). She can handle in the open court. She can create off the dribble in the post, as well as being able to post up over either shoulder.
I do not think Parker is a good comparison, either. Parker is more athletic that Stewart, but does not have Stewart's range on her shot (or her consistency from that range).
3) My player comparison for Breanna Stewart? Penny Taylor.
Taylor is a do-everything player for Phoenix. Though no player has yet to average 15 points, 5 rebounds, and 5 asissts for an entire season in the WNBA before this year, Penny Taylor has been the closest. She is the ultimate team player, in that she knows when she needs to be the start (MVP of the 2006 World Championships), but also when she needs to be #2 or even #3 because of the talented players around her. She is the consummate versatile player, scoring inside, oustide, nailing threes, hitting mid-range jumpers, driving to the hoop, using step-through moves, posting up smaller players, etc.
Looking at Taylor, she does not look especially strong or athletic. Other than being tall, you might not know she was a basketball player. But, at 6-1, she defends much bigger than her height (primary defender on Lauren Jackson when Phoenix plays Seattle), but also defends smaller guards.
Watching Stewart this past year, I saw Penny Taylor, only a taller version. The fluidity with which Stewart players is eerily similar to Taylor. Nothing looks forced; it all seems so effortless and natural. When Stewart needed to play #2 (to KML), she did. When Stewart needed to be the #1 option (Final Four), she was.
In Phoenix, we refer to Penny Taylor as "PFT" (Penny duck**** Taylor) or "The Ledge" (homage to her legendary status). When all is said and done in UConn lore and beyond, fans of women's basketball will refer to Stewart in the same way.
