The difference between ばかり and ところ is that ばかり means you just finished, can be 1 minute ago, 1 hour ago, 1 week, it really depends on what you are talking about. ところ means this moment exactly.
彼は旅行から帰ったばかりでも、また旅行する。 (Even though he just came back from his trip, he is going on another trip.)
帰ったところ、電話が鳴った。(the moment I got home the telephone rang)
The first example can mean that the guy came back from his trip a week ago and already goes on another trip where the second example really means the moment you got home.
As for 今, it just means now and can be compared to ところ, but a bit less strict with it being the exact moment.
The meaning of ところ also changes with which form of verb you use (past, present, future).
Past tense means just finished doing it, present means in the midst of, and future means just about to.
話すところ(going to talk)
I hope this explanation makes sense and answered your question.
When using ところ always put だ behind it, ばかり can be with or without だ.