You say you have done the calculations and both are within the limits so nothing anyone can add to that. The difference in cost is high but presumably you are aware of this. You need to consider your currency on type as always. The twin obviously being more complex in handling than the single. The Seneca props are uncomfortably close to the ground and so can be limiting in crosswinds if using the wing down method. Always be certain that the tyres are correctly inflated. In my book a strong crosswind in the Seneca requires a combination of only slight wing down and crab. Is the runway soft or tarmac: the Seneca has a tendency to pitch down during the take-off run requiring a good amount of back pressure particularly on soft ground - those low props again. Without sufficient practice and I mean practice these two things could be an issue. The winds and weather are generally very unpredictable in the islands. Research into the destination requires gaining some good advice from the 'Destination' wherever that is with regard to the local factors.
An old adage strongly held by some: never load a light twin above its single engine performance.