Antidepressants are not very effective (relatively), and even when you find one that seems to help a bit, most of them eventually lose their effectiveness. The most popular ones (SSRI's) aren't much more effective than placebo (something like 30%).
They're really supposed to be used as a temporary relief while going through some form of therapy like CBT or something similar.
I have tried just about every one of them, and side effects were terrible for most of them.
Everyone seems to react so differently to them, you really have to just try them out and see how you feel on them. Some lucky people get relief from them without much sides, but that seems to be very uncommon.
The thing I worry about is that most of these newer drugs are not well understood, their mechanisms of action and long term effects are unknown.
I personally had the most success with Remeron, but most people that I have talked to that have used it all experienced side effects that made it intolerable. Most doctors will prescribe an SSRI, that's what the pharma sales reps push on doctors, and that's usually the first thing they'll throw at a patient to gauge their reaction. I personally had terrible results with the SSRI drugs, and I tried just about every one of them. Tons of sides and only minimal relief.
I'm sorry to hear about your mother, hopefully your father will be one of the better responders to these types of drugs.