Licensing - QC Starter Edition has FULL license maximum of 5. You also canít purchase defect-only license for QC Starter Edition. So if you need more than 5 license, or if you need defect module only license (substantially cheaper than the full license) you'll want to go with the Standard Edition.
Modules Ė QC Starter Edition has Requirements, Test Plan, Test Lab and Defects. The QC Standard addition has the modules that QC Starter Edition has and in addition has Business Components module, Dashboard and also has advanced reporting.
Iím sure there are more differences, but these are the main ones I am aware of. If you can afford the QC Standard Edition, it is well worth the extra $$$.