Both of course. The more the merrier. Also, it depends on your purpose in having a tree. Most of us like to have our own personal tree. And Wikitree sure isn't that. It's a whole 'nuther ball game! ONE TREE FOR THE HUMONGOUS HUMAN FAMILY! Our own trees are just branches, leaves and twigs of the BIG ONE! LOL! So to "own" your family tree, Family Search is a fine way to do that because 1) It's free and 2) I remains out in Cyberspace for all eternity unless you, yourself delete it. There are other sites with free tree making capabilities. The two I can think of on the top of my head are MyHeritage,com and Ancestry,com. Being a diehard genealogist I love ancestry and have been a paid member since 1998 or 1999. I also own Family Tree Maker which was created by ancestry.com. It was recently sold to another company but FTM interfaces with ancestry.com so if I do research from my ancestry tree and save a record to someone's profile there, FTM and Ancestry sync so it goes right over to my software with one click of my mouse. I can also search from my FTM on my desktop.
On the other hand, if you happen to be an adoptee trying to identify birth family, the more places you put your tree on, the better-don't put all your eggs in one basket is what Grandma used to say and I think she was right.
One nice thing about Family Search is that you can research on their site. You can see the info in the record which is more than Ancestry allows for a free membership. But you can't see the actual record on Family Search unless you buy a membership.
While I am on the subject, a word to the wise about MyHeritage. While their trees are adequate, their DNA match search parameters are somewhat faulty. I was contacted by 5 people about our matches (I uploaded my DNA raw data from Ancestry to MyHeritage because I was searching for birth family). When we all uploaded to GEDmatch.com, turned out 4 were NOT even related let alone matching DNA with me!
Once you do anything on MyHeritage, they constantly deluge you with all sorts of enticing "We found something about your family" or "You have new DNA matches!" (yeah, 2nd-5th cousins-whatta' WIDE range!). And even if you unsubscribe they find some more "newsletters" to subscribe you to. My impression is that MyHeritage is a cheap imitator of Ancestry and an inferior one at that. They are all about the money, that's for sure. I don't advise spending any at that site.