I think it totally depends on the style of Gunging if I'm honest.
Certain sound effects we remember and relate link to gungings before. The Klaxon being so identifiable with a tank drop. Toilet flushes and fart noises with more slapstick style kids tv.
I'd say anything more "child like" the gunging/sliming/mess is looking like and themed like (which includes the attire, the setting etc) then the more silly the noises become
Oh man! Great question, can we have them all together at the same time?
It's too tough to choose for me as all of them have their place. Nothing hits the nostalgia button like the classic klaxon but there's something to be said for sounds that really emphasise the gooey sloppiness of the gunge. A lot of us don't have the chance to play around with sounds at home but I do think they can add a lot to the holistic experience if used well. Sights, sounds, textures, even smells can all heighten arousal and excitement when working together.
If you had to twist my arm... it's splats. I think... Ask me again tomorrow!
Weirdly enough there's something about fart sounds in combination with someone getting messy that really turns me on - I think they just really add to the humiliation / disgusting aspect to gunge that appeals to me