Ignoring Bournemouth for a moment... in the final games, Watford need to either get more points than Villa, or else get the same result but improve their goal difference by +2 (so if Villa win by 1 goal, Watford need to win by 3 or more; if Watford lose by 1 goal, they need Villa to lose by 3 or more). If they end up on the same points and goal difference, Villa stay up because of superior goals scored... unless we have an absurd situation such as Villa win 1-0 and Watofrd win 7-5 to level out goals scored, too... in which case Watford stay up because of superior head-to-head record vs Villa.
This all ignores Bournemouth of course. For them it's simple. They need to win and have both Watford and Villa lose... then Bournemouth stay up.
So yes, Villa look to have the best chance of staying up. But bear in mind they are playing West Ham who have taken 7 points from the last 9. Watford play Arsenal who, although the more difficult proposition on paper, have only taken 3 from the last 9.
All to play for!
Yes, I did not discuss bournemouth, in my comment but the writing error in the previous comment. As I mentioned, there is an advantage for Watford with an goals conceded which is also a point for the table. So I say, now Villa has +1 more than Watford, if Watford Draw and Villa lose 2 - 0 or more in the next match, then Watford will take over the position of Aston Villa. CMIIW
Edit:Watford and Villa are both on 34 points, so if Watford draw and Villa lose, the goal difference doesn't matter as Watford will be 35 pts and Villa 34 pts.
Basically Watford need to get more points than Villa, or if they get the same points then Watford have to improve their goal difference relative to Villa by +2 (so if Villa draw, Watford need a win as a Watford draw would leave goal difference unchanged for both teams).
Ignoring Bournemouth again
ah yeah my mistake, i forgot about that point, i mean if they are have same point in the end, the goal conceded by watford must better than villa.