Very difficult.
Much easier.
Both have their advantages and disadvantages. The boom system has much quicker connect times and the transfer rate is faster. However, once it contact, the receiver pilot has to work harder to stay in position due to a more limited range of formation position. Also, it requires an extra tanker crew member and the boom is large and heavy which requires it to be fitted to large aircraft only. Buddy/buddy tanking is not feasible - which is the main reason the USN stuck with the probe and drogue. You can't fit large aircraft on carriers! And the big limitation is that you can only refuel one receiver at a time.
Probe and drogue is harder to connect, but easier once in contact. Flow rates are less, but this is usually only a problem for larger aircraft as the hose can often transfer faster than a lot of fighters can take it. You can refuel multiple receivers. Also, with more operators using P and D, there is much more planning flexibility with allies being able to refuel each other's aircraft.