Here are my five cents, for what it's worth. You can always go with aftermarket turn signals, but then you'll have to find a way to mount them, so your best bet is to go with OEM. If you go with aftermarket, go with regular incandescent bulbs, don't go with cheap LED, they are usually very low quality and won't last. You will need a LED flasher if you go with LED, which is very easy to install.
If you stay with OEM turn signals and want to go with LED bulbs, the only good LED bulbs are Sylvania Zevo. They aren't any brighter than the stock incandescent bulbs, but they have the proper light pattern, proper contrast, and the instant on/off is nice.
For aftermarket LED solution, I love Kuryakyn Tracer turn signals, but they are only made to fit Harley housings. On my V Star 950 I actually replaced the stock Yamaha front turn signals with a set from a Harley, and installed these Tracer LEDs. They are very bright and look amazing. If you can find a set of Harley turn signals, you can always adopt them, and there are a lot of aftermarket LED options for them.
https://www.youtube.com/watch?v=utS0z1sEYNI