The reason I believe the God of the Bible is the real one, is because of actual evidence.
Multiple archeological discoveries have been made that support Biblical events, such as the flood and Noah’s Ark, the destruction of Sodom and Gomorrah, and the splitting of the Red Sea. The Bible also contains many prophecies of which quite a lot have been fulfilled. (search for Ron Wyatt and Kent Hovind for more on this)
Another thing I find interesting, is that the Bible says that the Sun, the Moon, and the stars were given to us, not only for light, seasons, keeping time, and a division between day and night, but also for signs. The Sun is about 400 times bigger than the moon, but it also happens to be about 400 times farther away from us than the moon. This gives us a unique experience during solar eclipses, and there’s no other planet (that we know of) that experiences solar eclipses like we do.
The way the Bible describes heaven and hell and how you end up there makes a lot of sense to me, other religions don't even come close when it comes to the afterlife.
And last but not least, I've experienced a few things myself that makes me belief that choosing Jesus was the right thing to do.
When I was little, my mom and I were going through a rough period when we didn't have much money. She was afraid we wouldn't have enough to get to the end of the month, so she prayed to God for help. Shortly after, some strangers with 2 big bags full of groceries came to our door and said that they needed to deliver it to us. Also, in one of the bags was a new watch, and "coincidentally" my moms watch just died a few days prior. Literally nobody knew about our shortage, nor about the broken watch, except for me and her, and we told nobody. And it was impossible for anyone else to notice too, because we didn't have much contact with family, friends or neighbors.
Another thing I experienced was way more recently, when I just started to believe and was starting to get closer to God. It was right before I went to bed, I went on my knees to pray and as soon as started, I heard the heating system in the attic go on and off, on and off, etc. We hadn't been using it for a few weeks because it was spring and the temperature was pretty decent. I ignored it and continued praying. It kept turning on and off for the exact duration of my prayer. When I was done, it stopped. Just to be sure, I went downstairs to check on the thermostat, and it was off.. like I thought. It was like demons were trying to spook me out because I was getting closer to God.
And last, tho it was my mom who experienced this, and not me. This was before I was born and before she became a believer (tho she thought she was a Christian, but in hindsight she wasn't). She told me that she bought some LP of the band Black Sabbath and listened to it at home. At night, when she was in bed, she heard footsteps and rumbling in the hallway and in another room. She asked out loud "who is there?" and the lights in her room began turning on and off, on and off, etc. She said something like "in the name of Jesus, go away" and the light went off and stayed off. My 2 experiences weren't as clear as this, and I know that this is weak evidence since I didn't experience it myself, but my mom never lies to me, she's the most sincere and honest person I know.
In conclusion, I believe that most religions around the world have their root in Ancient Babylon, which explains their similarities.
Why do I think Christianity is the only true religion and not one of multiple? Because Jesus says that He is the only way.
Here's a promise of Jesus that you might find interesting:
"He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him."
- John 14:21