If you have 2 similar players, I'd put my money on the multi-sport athlete. The thinking being that that player, because they have not played softball full-time, likely has a higher ceiling and is more likely to improve more once they switch to just focusing on softball than the player who has only played softball.
Sorry Greeny, I disagree. DD plays 14U. From February thru July is softball. Break in August. September - mid November is sofball. Then a break till February (with once a week practices). If she were to play 2 at the same time she most certainly would burn out; on sports in general. This provides her with good breaks and the desire to come back. Now she played multiple sports when everything was rec. But when she made the decision to play softball at a high level she knew she needed to play one.