You have to ask which type of cargo flying as well.
I have no experience with the courier cargo services like FedEx or UPS, but with general, long-haul wide-body cargo.
There are two major disadvantages to flying cargo:
1. The schedule might not be that fixed. Flights are often delayed because of late arrival of the cargo, cancelled because of lack of cargo, or changed completely in favor of cargo charters.
2. When flying pax, you most often leave your base to some destination, lay there for a day or two, and then fly back. When flying cargo, you can expect multiple sectors on most trips, e.g going to port A, then next day to port B, the next day to port C etc. Trips can add up to 8-10 days away each. It's ok if you're commuting, but if you actually live at your base, it sucks.
Now on the plus side:
1. No pax to deal with, keep them warm/cool, protect them from turbulance, appologize to them for being late etc.
2. Most airlines offer quite a lot of days off per month.
3. Pay is good.
4. Professionally speaking, because cargo planes are generally heavier than pax, the average leg is shorter. Less use of heavy or multiple crews, so you get to fly more. (some might see that as an advantage to pax flying, when you can sleep for 7 out of a 14 hour trip, and still get paid for 14)
5. Again, professionally, operation cargo airplanes, which are often older, and at high gross weights, mostly at night, I find challenging. Again some may prefer the pax all-new airplanes.

From what I gather, we cargo pilots are considered more adventurous, rugged pilots, going away for a week each time, and within that week covering 7 different cities, moving at night, using old equipment...
while pax pilots are the office-clerks in shiny suits, who never get their hands dirty.
Now you gotta choose what will you ride into town: a 1960 harley, or a brand new toyota?