Since you are a beginner, you may want to try a couple of computers first. Perhaps borrow one from a dive buddy. To me it is most important that you can utilize it under water - things are always easy in the dive shop or on the surface. This is especially true if you have to press buttons underwater while wearing gloves.
As it was stated earlier, your brain is most important. Though I have migrated up through the ranks of dive computers, I still dive with a set of tables and plan my dives from them. I have seen computers fail.
Think about the features computers offer and what you are looking/ready for. You may want to start with a simple bottom timer to track dive number, dive time, max/current depth, temp and ascent/decent rates.
If you do go with a computer, make sure you are comfortable with the algorithms used for dive planning and you are physiologically able to handle it. Computers may fail, but they never get bent...that I know of.
Dive Safe!