I don't know about Siggy. It really does just seem subpar to me. It needs three energy to attack, Darkrai decks will just catcher around it and Siggy can't even hit Darkrai that hard, and Zek Eels have Raikou EX to snipe around it. Those are the main two EX decks you'll be facing as far as I am aware and I just think Siggy is mediocre against both. It's downright terrible against other main decks like Empoleon Terrakion and Garbador Terrakion. Run one if you really want to but I wouldn't bother with it at all.
I do not understand why you would not max out Professor Juniper. Hands down the best supporter of the format and you'd run sub optimal choices like Cheren / Bianca over it?
Rest of the deck seems fine.