There are a lot of choices for slicer software. There is nothing specific needed for a delta printer (as opposed to, say, a RepRap printer).
The ultimate quality will depend on how well the printer’s firmware converts the gcode commands into servo movements.
If you are interested in free/open source software (it appears that you are), grab a bunch of the free ones and try them. I have 8 Marvins sitting in front of me that were printed with different settings and using different slicers (I wrote on their feet what I used and the appropriate settings). Test, test, test and see what works best for you.