There are a variety of reasons to choose (or not choose) a specific particular denomination or congregation over another.
Now, the reason to choose one at all is because it's generally considered important in Scripture and Christian practice to gather together with other Christians, and you have to choose some venue to do that, even if your criterion for deciding which one is just "it was closest to my house, and I deliberately don't care what denomination it is." I'm not going to answer more in depth "Why would I go to a church at all," that seems like a different question to me.
Selecting a denomination
But then there are a variety of criteria you can use to choose a denomination in general. A congregation is slightly different and I'll get to that next.
A given denomination might have specific theology or practice you like or disagree with. If you are very against the idea of homosexual Christians, for example, you might steer away from denominations that validate that. No denomination is likely to have 100% stuff you agree with, so this is a matter of degree. Do you like everything about the Churches of Christ but think it's silly they don't allow instruments in church music? Well, you'd decide whether that's a dealbreaker for you or not. Do you feel strongly about infant baptism, taking aspirin, divorce, contraception, etc? Well, various denominations are also for or against those things strongly, so you might decide to match up where there's meaningful parts to you. Does a traditional liturgy make you feel warm and fulfilled while singing songs on an overhead and jumping around leaves you cold (or vice versa)? Well, there's churches who practice each of those ways, so you'd probably decide on what you prefer.
And of course there are non-denominations. There are independent churches, though I think in general these still end up having a lot of similarities - are all the "independent Bible churches," if you visit them, more diverse than all the Catholic churches? Not in my experience. But in this case you can effectively skip the denomination phase and go to the congregation selection phase.
Selecting a congregation
When choosing a specific congregation, a given church home can vary more or less from the denomination's main theme. I went to a pretty conservative Epsicopal church for a time, for example. So the specific congregation's character may override the general denominational trends. One Catholic church can have very traditional services and another down the street can have a hippy-guitar-style kind of service. Maybe serving the poor is important to you, and that church downtown has a good soup kitchen ministry but the one closer to you spends the money mostly on youth outreach. So again you're back to some of the theology and practice questions. There are also a host of practical and social reasons. There may not be any churches of a given denomination in your town! Fellowship is one of the goals of a church, so you may attend a congregation because family or friends (or someone who can give you a ride, etc.) do. Praying about it and letting the Spirit help lead you is also recommended.
Choice, A Sticky Wicket
Some people have strong "brand loyalty" - they really identify with one denomination's teaching or one church home and it gives them strength to have a history with them. Some people don't - I am of this stripe. I was raised Methodist and in college was a Presbyterian youth minister, went to Episcopal and Lutheran churches regularly and visited others, so now when I move somewhere I visit churches from the set of denominations I find generally congruent with my understanding of doctrine and preference of practice to find good congregations (More conservative than normal Methodists or Episcopalians or more liberal than normal Lutherans, traditional with a bit of evangelical to them).
I have heard some argue that there is too much choice in churches in America today (similar to the paralyzing and polarizing amount of choice in consumer products). If the capital-C Church of all the believers stratifies into sub-groups that all effectively believe the same, are you missing out on being challenged? Would the church be more functional overall if it had all the types/spiritual gifts represented? Some denominations like the LDS and to a lesser extent the Catholics stress this by saying you really should attend your neighborhood church and not be such a picky shopper, which is a fair point.