Evaluation of Inquiry tools; Survey

I am using mainly three inquiry tools for my research.
.
Which is Survey, observation, and Interview.

I would like to analyse and compare these tool`s advantage and detriment.

Survey.

Advantage;
I have actually used a lot of survey for my research.
However, it does not mean it was successful!
I used a lot because I found it quite convenient and time saving, as once survey has giving to people only thing I needed to do was to wait.
Also, surveys results are much easier to check and analyse compare to other inquiry tools results, because it has been done by people and there are evidence on the survey.

 Observation and Interviews, I need to listen to the record or read through the notes to recall the memory of that time.
And, human memory can be effected by day to day incidents.
For example, let`s say I interview some one, and that person gave me generally negative answers at that time. And, I analysed as that person is not enjoying and also finding hard to carry on with what she does. However, later on I find out that her mother is very heavily sick, so that effected her answers and my understanding towards the person.
With circumstances like this, I find it hard to analyse corrcetly when I go through the results of these tools.

However, survey results are pretty much one dimensional and straight forward. That is why I found much more simple and easier to analyse on survey.
And, names are unrevealing, so I will never know who is who. So, there are no space for emotions to effect the results.

Detriment;
is ironically all the advantage above. I found these advantages can be back fires in survey.

Most importantly, Reliability of information.
I used survey on the web; using survey monkey website. And, also I made some questionnaireｓ to give to people.
The reason I avoid survey monkeys and instead I gave out the questionnaire was, because some of the students are not old enough, so I felt very inappropriate to ask them their e-mail address and fill them up on the web. 
I made that decision based on my ethical knowledge of teaching young dancers.
However, I have noticed the difference of answers between web survey and questionnaires.
The questions were the same, and I have asked the students there are no need to reveal their name.
However, when students were filling in  questionnaires, I could clearly see the appearance of teacher effect their answers. 
I had a feeling of they are worried and thinking of consequence, so students did not answer entirely honest.
Even, though name is not known. 
However, I guess there are evidence on the paper. So, I do I understand why students found it hard to express freely.  
Survey monkey results were much more direct and some of the answers were very useful for me to improve my quality. However, the problem I had with survey monkey was I did not receive reply as much as I wanted to.
As I mentioned in advantage section, Yes, it is time saving in a way compare to interviewing people  and observing classes and people` behavior. However, the problem is once the survey has given to the people, only thing I could do was to wait for the reply. 
I guess, I can nudge people to reply me, but I do not think that is a right way to get a reply for the research.
No wonder, all the restaurants give out a lot of prizes and money to fill up the survey!
That was the biggest dilemma with survey monkey.


Do people find it same?
Or does any one have any good solutions?