I'll talk only about focal lenght as I mainly use manual lenses. This is a matter of taste... On APS-C: - I don't like 50mm lenses (75mm FOV) because I find it too long for general use and a bit too short for portrait and bokeh. It works, but I prefer slightly longer. I must admit 50mm macro lenses are very useful. - 55 / 58mm lenses are almost equivalent to 85mm FOV. I find them better suited to my taste. Good bokeh, long but not too long. But they are more expensive and usually less good than their 50mm conterparts. Hope Samyang will offer something in that range, such as the Sigma 56mm for Sony. - 85mm lenses are about 130mm FOV. Not very interesting because they usually have long minimal focus distance, they are also quite big and heavy. If I had to pick one, would be the new Samyang for APS-C. - 90mm lenses are often macro ones, that's why I like them on my Fujis. They are a bit heavy thought. I shoot mostly macro but some are great at infinity if you need something a bit long. - 100/105mm lenses are often very good and cheaper than 85mm. Started to be really long. - 135mm lenses can be tricky to use hand held wide open. They are cheap and good. Very long for me. If I had to choose one lens, would be something between 55 and 58mm. 55 macro or bright 55-58mm lens depending on your likings.