What is the of your community? (e.g., hobbyist group, business networking, fan site) Do you plan to launch dedicated mobile apps ?
Customizing PHPFox is often described as "working with a black box." The encryption of certain core files in past versions made deep modification difficult. While recent versions (v4+) have opened up, developers often find that creating a plugin requires hooking into specific, sometimes undocumented, points in the core. The theme system uses a proprietary template engine, which can be a learning curve for new developers. phpfox vs socialengine
SocialEngine is generally favored by freelance developers and agencies for ease of customization. What is the of your community