The problems with conflicting advice

I've discussed this issue on a writers' forum yesterday. Though I think editing, rewriting and tweaking is essential, I see a lot of writers having difficulties with conflicting advice. Thinking back to my early days, I had comments on my book on what to change, what to delete, what to pad, etc. I personally was relatively sure what I wanted and didn't get confused; my story hasn't changed one bit, but I see others change their ms after each comment they receive, often until it's beyond recognition.
The problem is: it's all down to preference. Someone doesn't like first person, present tense, don't go and change the whole book into past tense. Some think a particular scene could be deleted, some don't. I guess what I'm saying is that you have to stick to your guns, trust yourself, listen to the advice and ponder, but don't change everything that someone suggests, unless it really makes sense and you love it even more after the changes.
Many beginners are insecure and listen far too often to others than to their instincts. People talk differently, in different speech patterns, the more you try to please those who criticise, the more you're losing your voice. 
I, for instance, have sent out my literary fiction novel to five people. Two only wanted to do me a favour, but it was clearly not for them, one got back with suggestions that would alter the whole concept of the book, one got back with excellent suggestions and the confirmation for what I had the feeling might be wrong: it lacks 'excitement' in the middle part, and one loved it so much to actually pass it on to an editor who loves it equally.
I've had men and women reading the book and I got valuable feedback from all five readers. It helps to know your writing, your voice and to see where the changes might affect it. Step back from your ms and think as a reader for a while, would you be excited by the book or do you think it could be improved? Get advice from a hand full of people and take every comment into account. I've once posted an excerpt on facebook and someone went to rewrite the whole scene. Though well-meant it wasn't my voice anymore.
What I look for are suggestions that make the story stronger, not the voice. Some people who mean well, but don't know how to critique will start fiddling with your wordings, change your vocabulary and the way you write in general and they will start correcting each other; if you start listening to those, you'll easily lose your voice by changing it back an forth. 
Same goes for the so-called 'rules' in writing. Some people will try to edit everything out of your manuscript, adverbs are not bad, you just need to keep them under control. I see those 'rules' as guidelines, not as set-in-stone rules to follow. Though you should know the 'rules' to break them. 
Best is to have mentor who will teach but doesn't influence you.