The IELTS is administered as either a paper-based test (as its classic form) or as computer-delivered test (since recently).
This difference concerns only the first three section of the test: Listening, Reading, and Writing. The Speaking section is always administered as an interview with a professional IELTS examiner.
Both versions of the test take place in an official IELTS center and are scored identically. The only technical difference is the length of the test: the computer-delivered test is 10 minutes shorter, as there is for need for the answer transfer time in the Listening section.
The choice of the test administration is up to the test taker and usually depends on the seat availability at the IELTS center in a particularly region.
In terms of IELTS preparation, there is no difference between the paper-based and computer-delivered tests.