Which phrase is most likely to be part of an effective thesis statement? I think
Therefore
I believe
In my opinion

Therefore is the strongest term you can choose because it makes your writing sound formal and it shows that you aren't trying to say, "I hope you get what I'm saying." It instead shows, "This is what I strongly believe and these are the facts to back it up." So I would say "Therfore" is the best part of a good thesis statement.