I'll be spending a lot of time focusing on the evidence for evolution and against creationism, so it's worth explaining why I don't just accept theistic evolution (TE) as many Christians do. I'll leave aside my other objections to Christianity while answering this question.
TE takes some or all of the Genesis creation account to be allegorical. The problem is that there's simply no reason for an allegory here. The creation account itself doesn't teach us anything morally – certainly nothing that an omniscient God couldn't teach us using a more accurate account. (And while the Adam/Eve part of the story does offer a moral lesson, we'll see later that this portion is definitely meant to be historical.) Objections that the Bible isn't a science textbook are pointless; one expects accuracy from any text unless there is a legitimate reason to stray from the truth.
Some might say that the real science would only confuse people of that time and distract from the message. But first of all, I would expect an omniscient God to be able to express himself accurately without confusing people. And second, the creation account differs unnecessarily from reality on too many points. For example, in the creation story plants come before stars and birds before other land animals, when in fact the orders are reversed. There's simply no reason for them to be out of order; the accurate version would be neither distracting nor confusing. There's also no reason to make bizarre mentions of nonexistent phenomena such as "waters above the firmament." Clearly, the creation account is the way it is because the authors believed it to be literally true.
Another problem with TE is that biblical support for the creation story isn't limited to Genesis 1–3. For starters, it's quite obvious that the Bible intends Adam and his descendants to be real people. The Genesis 5 genealogy stretches from Adam to Noah, and Luke 3:23-38 traces Jesus' ancestry all the way back to Adam. Here are more verses that seem to take creation literally:
- Exodus 20:9-11 and Exodus 31:15-17 make no distinction between the "days" of the week and the "days" of creation.
- In Mark 10:6 Jesus says that "from the beginning of creation" God made humans male and female.
- Romans 5:12 and 2 Corinthians 11:3 clearly show that Paul believes the snake/forbidden fruit part of the story to be real.
- 1 Corinthians 11:8-9 says that "man is not from woman, but woman from man."
- 1 Corinthians 15:45-47 says Adam was "the first man" and "made from dust."
- 1 Timothy 2:13-14 says "Adam was formed first, then Eve" and that Eve was deceived.
- Hebrews 4:4 says God rested on the seventh day – again no indication of the day being non-literal.
Incidentally, Noah's flood is also seen by later authors as historical:
Romans 5:12 above also states that death entered the world through Adam's sin. This is totally incompatible with evolution, which states that billions of creatures died before the first humans evolved. TE advocates' attempts to resolve this by suggesting that sin also caused death "retroactively" stretch credulity well past the breaking point.
As I've shown, the entire Bible treats the events of Genesis as if they actually happened. In my opinion, it does not leave TE open as a legitimate option, so my choice is between creationism and unguided evolution. Based a thorough examination of the evidence, I must choose the latter.