RIP Whispy Woods.
A Titan vs. Alucard fight would pretty much destroy that entire forest, Mr. Woods wouldn't have an opportunity to watch the finale of the match, which honestly could be very quick or very long pending how the fight goes.
Eren needs to go Titan form immediately if he even wants a chance. His human form would fall pretty quickly to Alucard's speed and weapons. Alucard likely would give him a chance to transform, as he would grow extremely bored of the fight from the get go and loves a challenge.
So Eren in Titan form vs. Alucard. We've seen Alucard can change his shape and size at any time so the size discrepancy could be evened out immediately if Alucard wanted. Titans can show burst of speed but I don't believe it to be on an inhuman level like Alucard so he should be able to out maneuver the Titan with ease while dodging any strikes Eren throws his way. Alucard blasts away at the Titan, not doing as much damage as he would like. It's at this point he would put his guns away and go hand to hand, likely increasing his size to match the Titan. A thrust through the chest would likely hurt the Titan, but not kill it. Eventually Alucard would target the head and decapitation would likely follow for Eren, and devoured for later usage.
If Eren goes Titan form it will be a long drawn out battle, but the Titan doesn't have the speed to match Alucard in my opinion so even with its impressive strength it does no good if it can't get near Alucard, who also have superhuman strength on his side to counter. I see it being a longer fight only until Alucard figures out Eren's weakness and takes advantage and chops the Titan's head off with his bare hands to move on to the next round.
