Can I suggest neither?
Both have their advantages of course. As above.
I thought about both for my 240 reef, and had UV on my old freshwater.
I have neither.
From my experience everyone I have talked to, the hassle / risk / expense was really not worth it.
Without BOTH enough dwell time and turnover, both are useless.
Which for a 300G means some sizable equipment.
Ozone is tricky to get the flow right, and dangerous if vented wrong.
UV lights need replacing a lot and use up quite a bit of power.