Both ships are identical so no choice between them, so it is purely down to itinerary. Personally out of the two I would take the Western route as at least you get Cayman and Mexico [so you get a hint of being in a foreign country!]. Eastern you just get St Marteen and St Thomas which has about 5 cruise ships in a day and is just a mass of shops trying to sell you diamonds IMHO!
I think the Southern route is best though.
I think that this is another occasion when I agree with our correspondent from Newbury, Liberty and the West Caribbean gets my vote. I would also say that if you can afford the time and the money a short extra stay, pre-cruise, in Miami can help acclimatise with jet-lag and weather although I much prefer Fort Lauderdale it's still an interesting stop......Nei.
Gee thanks Neil! To the OP I guess you are constrained by dates, otherwise you are aware that Freedom and Liberty both do alternate weeks eastern/western.