Microsoft PowerPoint is the most commonly used software for creating posters.
Apple Keynote, Adobe Illustrator, and free/open software options such as LibreOffice Impress and GIMP (GNU Image Manipulation Program) can also be used to create academic posters.
Most conferences and meetings have size/dimension requirements. The most common sizes are 36” tall x 48” wide (horizontal or “landscape” orientation), although other sizes are also typical.
Usually the cheapest option, quick turnaround, but can be cumbersome if traveling on a plane
Can be more expensive and may require more lead time, but great for travel!