What strategy will get the most distance for Home Run Contest?

Just do as much damage as possible to the sandbag as possible before winding up with the baseball bat.

I myself have found stronger characters work better then fast characters. I got 2000+ ft. with King Dedede by hitting a spike ball at the sandbag repetitively until damage was about 80%-100% then using the baseball bat to deliver the final blow. If your final percent after the final blow is over 119% then you are practically guaranteed to get over 2000 feet.

Edit:

Another important thing that I just realized is the position of the sand bag the further right on the platform it is the further the sand bag will go. I've seen the same damage count on the sandbag yield two very different distances based on where the sandbag was.

As Ganondorf, without moving and timing it perfectly, do down smash, down smash, forward smash and bunch of forward tilts consecutively until you have to grab the bat then hit it perfectly at the tip. Got me 3,608 ft.

The trick is with Ganondorf but not those is smashes.

if you drop the bat and it hits the opponent he will pick it back up automatically. so I suggest trying that over and over and then smash. I have seen people get up to over 7000 using that strategy.

Ness. Get Sandbag on right, spam pk fire and swing bat at 2 seconds. Should net u 2 to 3.5k feet

With version 1.0.8 comes the costs-money DLC character of Roy. Roy can get over 5,000ft easy peasy. Just do a bunch of f-smashes and f-tilts, and when the clock strikes 4, start charging Flare Blade (neutral special). Just when the clock hits zero, the move should detonate for ~50% damage and massive knockback.