The Foxit reader, according to the review, is larger than Sumatra PDF reader, but a good bit smaller than Adobe Reader's footprint. It also has more functionality, allowing markup and annotation. Unfortunately, if you save the annotated PDF, Foxit places an advertising banner on the front of the sheet. The pro version (read paid) does not add a banner to the first page.

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Foxit is also only available for the Windows operating system. Prices for the advanced versions of Foxit are listed on the linked page, and you are able to pick and pay for only the functionality you need for your PDFs. The complete Foxit PDF suite is much cheaper than Adobe Acrobat.
Image from Foxit software site.