IPA ok for now, pointless later on.
To be honest if you're just starting your initial training, it doesn't matter which you join, because the only useful thing either will provide is an overview of the employment situation. I was a member of the IPA and I found it quite good at this stage in my career, perhaps more so than BALPA. And it's true that the IPA gives one the personal touch.
Once you've qualified and got that much sort after job, things change. Now the name of the game is to protect and hopefully enhance your working conditions, pay and benefits. Assuming the airline in question has collective representation agreement with their pilots, and all the ones worth working for do, being a member of the right union becomes very important because your reps can only have a strong negotiating through strength of numbers and a general resolve amongst members to achieve their aims. You will be doing yourself and your colleagues a disservice if choose to a union other that that with the collective representation agreement. Save one airline, IPA/IPF doesn't have any of these and I can't honestly see it displace BALPA from any other airline.