It's what really works best for you should be the factoring choice. Me personally I prefer Simple Portal but everyone has their needs and each product serves it's specific purpose so it's really what will work best for you.
Xenporta has little or no support although there always seems to be vigorous posting on its thread, which \i think is users helping each other. Many sites get very good results using it.
Simple Portal is efficiently and pleasantly supported by @ExtraLicense. There has been a lot of response to what users want and that looks set to continue. The addon clearly has a pragmatic and flexible approach, eg working with the Widgets addon.
Conclusion if you are knowledgeable as a tweaker of code, and you like the look of Xenporta's features on its user sites, try it. If you have little knowledge of code, and see support as an essential security, use Simple Portal.
A third possibility is Xenzine Articles, which presents article pages (with linked discussions like the RM)with an attractive display of graphics per article on its listings pages. It has Top Articles, and Recent Articles, Categories, and can work with sidebar Widgets. It does not yet have a homepage design but this is clearly on the way.