Caulking or wood filler

[Ukman2021]

I've just built a TV and fireplace recess unit using mdf. Some of the mdf boards were cut to short and there is little gaps between some of the mdf boards within the shelving unit, should I just use caulk to fill up the gap or would I have to use wood filler?

Also where the mdf boards meets don't want the joints to show once painted, is caulking, then sanding best?

Many thanks.

 

[HERTS P&D]

Car filler/2 part filler is best.

Andy