These cards aren't as bad as they may look. Sure, playing cards that help everybody aren't always the best, but these cards create a very tenuous peace within the game. When everyone has access to a power like that of Wishmonger's, people are less apt to use it since anyone can use it. It's also a rather big sinkhole for mana since each ability costs 2 to activate. However, some of these are better than others.
Probably the weakest of the mongers, Sailmonger will pretty much be useless since your opponent will give a creature flying and then you'll just give one of your creatures flying in response. Unless you have no mana available of course.
Pros: Gives creatures flying for 2
Cons: Useless as evasion if your opponent has mana available.
Basically, this card equals no hands for anyone ever. Everyone will use this card's ability to make sure that no one else has cards in hand. Easily the second strongest monger.
Pros: Colourless discard
Cons: No one, including you, will have a hand
These cards aren't that different from each other, except that they affect different creatures. They are token control in essence. Cards like Rhys the Redeemed and Talrand, Sky Summoner hate cards like these because they can easily counter their effects, along with dealing damage to players. They're like Pestilence on a stick!
Pros: Almost like Pestilence
Cons: Doesn't effect certain types of creatures
The best of the 5 by far but also the most dangerous since it can give protection to anything. The worst part is that even if you were to use it on something that wasn't yours, you don't get to choose the colour; the controller gets to pick. Very dangerous indeed.
Pros: Gives creatures protection from colour of its controller's choice
Cons: Anyone can use it