Now I know a lot might not have noticed but as a huge fans of both shows, I noticed that there a lot of similarities between the two shows.
1.both set siblings who fight the evil supernatural (demons/vampire/evil witches...).
2. both set of siblings save/protect people in the expense of their own lives.
3.both set of siblings lost their mothers at young age to the supernatural.
4.both older siblings became angel death for one day (Dean) & (piper)
5.both younger siblings had visions of the future (Sam) & (Phoebe)
6.both younger siblings went to the dark side/became evil.
7.both younger siblings slept with/had a relationship with demons
8.Dean turned into a vampire and was cured, Paige turned into a vampire and was turned back
9.both set of siblings had a half sibling (brother/sister) they didn't know about.
10.both set of siblings lost a sibling (dean & Sam lost Adam) (piper, phoebe & Paige lost Prue)
11.both set of siblings have/had guardian angels (Castiel) & (Leo)
12.both set of siblings died multiple times and were brought back to life.
13.both set of siblings traveled back to the past and traveled to the future.
14.both set of siblings know hand to hand combat and martial arts.
15.both set of siblings had/have generations of hunters/witches who fought the evil supernatural.
16.both set of siblings cast spells.
17.both set of siblings been to Jail/prison more than once.
18.both set of siblings had interactions with fairies and cupids.
19.both set of siblings fixed/rebuilt their homes multiple times, the Winchesters (the Impala) the Halliwells (the manor)
20.both set of siblings had a book/a journal to help them fight the evil supernatural.
21.both younger siblings choose a demon over their own siblings, and were quickly forgiven for their betrayal.
22.both set of siblings had/have reputation in the supernatural world.
23.Misha Collins, Mark Sheppard, Kurt Fuller, Charisma Carpenter, Billy Drago, Emmanuelle Vaugier, and Sebastian Roche were guest stars/regulars on both shows
24.both set of siblings dealt with the seven sins
25.both elder siblings(dean, piper) became death/reapers for one day.
I think that's all, please if there's more tell me in the comments and I will add them to the list.