这个句子有几个简洁和雅致的表达方式：
Regular classes will be much more efficient than online ones.
Regular classes will have much greater efficiency than online ones.
The efficiency of regular classes are much greater than that of online ones.
Regular,as opposed to online classes,will have much greater efficiency.
我觉得第 4 句 最佳.
3个建议：
1.考虑用 classroom classes 替代 regular classes
2.加个单词 generally 使句意比较委婉,比如：
Regular classes will generally have much greater efficiency than online ones.
3.我觉得 greater efficiency 比 higher efficiency 贴切
我是加拿大人,前英语老师.