It would be ARod and by a wide margin mainly because he's going to play every day as opposed to once every five days. I wouldn't call it a wide margin. You didn't take into consideration the impact each player would have on a game. Since winning is about scoring more runs than your opponent, lets assign 50% value to runs scored and 50% value to runs allowed. Lets say team defense has 20% to do with allowing runs and pitching has 80%. Therefore multiplying by 50%, defense has 10% impact. Pitching has 40% impact. Out of pitching we have starters and relievers. Lets say the average starter goes 6.5 innings (pitches 72% of the innings). So he has 72%*40%, roughly 29% impact. So, in a 5 man rotation, 1 starting pitcher has about 6% impact on the game. As we stated, runs scored have 50% value. You could divide that by 9 (or 8) and youd have about 6% impact assuming the player plays every day. A little bit more (~1%) added for defense. So, basically a starting position player pretty close to as valuable as a starting pitcher. The position player plays more often, but has a smaller impact on the outcome of the game. Note: this is quick and dirty with assumptions. Theres probably some interesting things you could add with win shares, leverage index, positional value, etc. The main other things to be taken into consideration is who they would be replacing, $, players to give up in a trade.