I believe AA is the only one of the 3 that provides complimentary upgrades at all on this route (complimentary to EXPs and with 500 mile certs for Plats/Golds).
UA requires the use of RPUs, miles + cash, or cash to upgrade on this route but anyone can use RPUs.
DL requires the use of RUCs, miles + cash, or cash to upgrade but I believe only you can only use RUCs if you are a Diamond (a Platinum with RUCs can't use his/her RUCs on this route).
My suggestion is try and get the $599 advance tickets on JetBlue Mint, it's the best product and the best price.