I agree with Neil. Ryanair and easyJet have different business models. However, other smaller airline will compete with one or the other. For example, Vueling's business model is closer to easyJet's one (I think so, didn't travel with them).
To the OP: Ryanair flies to further, smaller airports. As you have a short time in each city, transfers are longer (except for Rome, CIA actually closer than FIU, and public buses are available). But AFAIK for Barcelona and Paris, the transfer time is quite long. And consider the price of the bus in your budget. It was €15 one way in Paris (the most expensive AFAIK).