Japanese people say “Eto”/「えーと」 or “Ano”/「あのー」 very often in daily conversation. You can translate them into “Umm” in English. We say them to keep the right to speak in a conversation. Is there difference between “Eto”/「えーと」 and “Ano”/「あのー」? In conclusion there is no big difference in daily conversation. Japanese people wouldn’t use them differently depending on the situation, but some people would say there is the following difference between “Eto”/「えーと」 and “Ano”/「あのー」.
Some people would say Japanese people use “Eto”/「えーと」when they fill in the gap in conversation, search memories, stories or words from the deep point in their brains and calculate something. I will introduce an example as follows.
A : Would you like to go to watch a movie next Saturday ?/「次の土曜日、映画を見に行きませんか？」
B : Umm… yes, I can go next Saturday./「えーと、はい、次の土曜日は行けますよ。」
In this case the person B tries to remember his plan next Saturday while saying “Eto”/「えーと」.
Some people would say Japanese people use “Ano”/「あのー」when they fill in the gap in conversation and look for expressions although they already decide what they would like to say. I will introduce an example as follows.
A : Would you like to go on a date with me next Saturday ?/「次の土曜日、デートに行きませんか？」
B : Umm…. I’m sorry. I have an appointment next Saturday./「あのー、すみません。次の土曜日は予定があります。」
In this case the person B already decided to reject that and he is thinking how to reject while saying “Ano”/「あのー」.
Some people would say there is a difference between “Eto”/「えーと」and “Ano”/「あのー」, but in daily conversation they have almost same meaning and Japanese people just say them to keep the right to speak.