Good alternatives? I don't think so, hence the lack of a long list of options provided by forum members. The problem is, there isn't a competitive market for "viewers". Editors, creators, databases, yes. Viewers, no.
Pretty much anything you could replace the image viewing function of Preview with is designed to do much more than view, and costs money, which makes it a less than good replacement for a system provided (free), well integrated, image/pdf viewer with light editing features.
Pixa provides viewing, conversion, tagging, and resizing functions for images and lesser functions for pdfs, but it's primarily an image database, so items must be added to its database before you can view them with Pixa.
iPhoto is a pretty good viewer and light editor, but it has the same "database" issue as Pixa.
Any graphics editor will do, like Acorn, GraphicConverter, Pixelmator, or Photoshop.
Personally, I like the "buy a trackpad" option. The gesture bus left the station a long time ago with Apple. It's only gonna get harder and harder to use a Mac and not adopt gesture based navigation.
