If you have not watched Neil Degrasse Tysons on this one you really should. This is just one example: [bing.com]

It would be silly to believe we are the only life in the universe. Other life is possibly out there but I don't think that Martians are dropping in. When I became atheist I chose not to believe something without evidence. Aliens and anything supernatural fall into that category because god belief in a biblical sense is supernatural. I have no more evidence of ghosts than I do of devils or gods. Nessie and Bigfoot may be possible, but I have no evidence of them either.

I went with "they absolutely do exist." But that does not mean that I think they ever came here. Assuming that faster-than-light/warp drives/et cetera are even possible, it's still an impossibly huge universe and we are a mere speck on the edge of an unremarkable galaxy.

I'm put off by the term 'alien'. Little green men with big heads, probably not. Per the definition of "life": 'the condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change preceding death.'

For the most part I believe there is life out there. But to what capacity, past or present, I do not know. To our knowledge of life on Earth, it is complex but it has happened. With the vast expanse of the universe and the incomprehensible amount of time that has passed from the beginning to now I believe that there could have been, or could be, a moment for life to have been created. I also think of life as something extremely simple. Such as Mycoplasma. [en.wikipedia.org]
or "ultra-small bacteria" [sciencealert.com]

Anything more complex than that I could only hope.

Depending on what you are asking my confidence level would change. I am about 99% sure that their are alien life forms out there. Intelligent life is less probable and intelligent life that has advanced beyond us even less. That being said, this is not something I put a lot of time worrying about until we have more evidence. I do think it is interesting, but currently there it is not easy to find answers, so I will reserve judgment. Sadly, I don't think I will get a satisfactory answer in my life.

They are the gods, worshipped by dumb mankind

I think it is possible that they may exist, but due to distances and time relativity issues, I doubt we will ever meet any.

I think it is far more likely to meet peopel from other versions of our own planet in the multi-verse, at least by our current undert understanding of hte universe. The problem with traveling the multi-verse though was highlighted in that old (and slightly cheesy) TV show "Quantum Leap", only unlike the TV show communication between alternate universes would be very unlikely, but it still woudl be difficult to get back to one's universe of origin just the same. In fact it would be highly unlikely (as in a statistical impossibility) a person would be able to return.

I'm going to say there's a high probability of life on other planets but I do not think any of them have visited this planet.