What is the best research method?
Or ones that have been successful for you?
Thank you.
I imagine you’ll get some better responses i you say what you are trying to figure out.
Are you a student? a professional designer? or just learning the field on your own?
this is similar to asking what type of color to use in a sketch, very very broad.
what are you trying to achieve specifically?
Contextual inquiry (end-user observation)
Usability testing (simulated environment)
Human factors/ergonomic evaluations
Market research
Safety and efficacy testing
Clinical trials
One-on-one interviews
Focus groups
Secondary research
Pretty much in in that order except for secondary research. That seems to be done continually throughout any project.
Research is for people without enough balls to design with their gut! 
har har har… lol
takes a lot of bravado to tell your boss, who cares what your “so called researchers” think these a-hole customers want, I’ve got what they want right here [makes inappropriate genital grabbing gesture]
I wonder if that will get censored?
Seriously though check out “a designer’s research manual” by Jeniffer and Ken O’Grady. It’s a pretty good introduction into available methods, so you can pick which you need to use and then go research it in depth.
More like, not enough empathy to design with their hearts.
In all seriousness, methods depend on the project. Sometimes an ethnographic study would be most appropriate, other times a generative study would yield more actionable findings. Over the course of an entire development cycle you’ll almost always use multiple research techniques so it’s hard to say which single practice works best.
On a broader sense, I am a proponent of user-driven, participatory design rather than an expert, designer-driven process. I don’t have enough experience to defend that position, it’s really just where my education took me.