A common question from newer players is what is the easiest character/build with which to play the game. Easiest is subjective, so you'll get a few different opinions as to what character/build you should start with, but I'll give it a go. This is purely PvM questing, no PvP considerations taken.
The Fishymancer is the stable of this character and a normal starting point for most players. This build is completely item independent and could solve Hell naked if necessary. With 20+ minions doing the dirty work you'll find yourself in personal danger infrequently. Going can be a bit slow and tedious, but you will encounter few, if any, monsters that are immune to your party. Since this character can load up on the MF he makes an excellent runner of areas in search of equipment for the rest of your planned builds.
Other builds are possible with the Necromancer, but the choices are fairly small and the rest are more difficult and definitely more item dependent, such as the Dentist.
There are many more options for this character, all relatively the same as far as ease of play is concerned. Popular choices are the Meteorb, Blizzballer, pure Blizzard and pure Lightning sorceresses. The first two make excellent all around MFers and can solo any part of the game due to dealing multiple types of elemental damage. The second two are more specialized in that some areas they will be relying purely on their mercenary to deal with all encountered monsters. This makes questing with them more difficult, however once done they are faster boss runners than dual elemental builds.
They are fragile creatures however, so care must be taken to keep them out of harms way. Thankfully they have Teleport as a skill that allows them to run away from danger, or reposition their mercenary companion at will. Therefore it's suggested that an Act II mercenary is acquired, as you'll need a durable tank to keep the monster packs at bay and the aura these mercenaries have (Defiance, Holy Freeze) are invaluable to that end.
This character is the most versatile of all the classes, and has the most possible builds available. The easiest build type would be any of the Zealot types, or the Hammerdin. A plethora of auras for all occasions ensures the Paladin is not without a means to deal with most situations and Holy Shield ensures his survivability is high with a decent blocking ability.
Both types mentioned above require very little skill switching. The zealots (Frost Zealot, Tesladin, Fanaticism enhanced pure Zealot) are pure click-and-hold until the monsters are dead type fighters. The Hammerdin is similar in that he simply spams fields of hammers and waits for monsters to wander through and kill themselves off. The zealots have some issues with immune monsters in Hell and therefore require backup skills, while nothing except a single monster in Act III (Wailing Beast) is immune to the Hammerdin (which is why he's so popular).
The Hammerdin is fairly item independent, as are the elemental zealots. On the flip side the pure Zealot does require a high damage weapon to be effective, and so is the most difficult of the zealot types to equip.
The easiest of builds for this character would be the Trapper (Lightning or Fire). Simply cast Cloak of Shadows, lay traps and wait until the monsters are all dead. Move forward, rinse and repeat. Not the most interesting play style but simple.
However on the flip side the Martial arts builds (Phoenix striker, DTail Kicker) are much more difficult. Due to the number of skills used they are being switched constantly so great attention is required to ensure the correct number of charges is obtained and the right type of attack used, all depending on what immunity the monsters have. More intense than almost any other build type and fairly item dependent to boot.
Both styles have access to an effiecent companion in the Shadow Master. Just keep an eye on her, as she is know to convert some of the monsters from time to time. They can't be hurt by you, but don't bypass them as they will turn on you again once the conversion wears off. You don't want enemies both in front and behind you if you can avoid it.
This character also has a fair amount of possible builds available, the easiest being the Lighthing Fury Amazon and the Multishot/Strafazon. A pure LF build can deal with most packs (LF) and all bosses (CS) within seconds and has the needed backup skills (Jab, FA...) to take on the LIs as well. This build is very item independent as her damage does not rely on how good a weapon she
wields, since it is all elemental and always hits the target.
The Bowazon takes on enemies from afar and with skills like Knockback and Chance to Flee ensures no one ever gets close. She is more fragile than her melee sisters so take care in where you stand and be aware that with Strafe you are locked in place until your round of arrows are away. She is also more item dependent in that a high damaging bow is absolutely necessary and certain mods (Knockback, leech) are highly desired.
What makes these builds really shine though is that the Amazon has access to the best tank in the game, the Valkyrie. Along with that she has an excellent scout in the Decoy that can be cast far ahead to see what monsters/dangers lie in wait.
Druids have a limited number of simple builds available. The normal ones are fire, wind and werewolf/werebear. The Fire and Wind druids have excellent tank options in the form of a summonable bear or a pack of wolves. However their skills are not the easiest to aim, especially Armageddon, so there is a learning curve. Cold and fire are the two most common immunities in Hell, so a backup plan is required to solo the game.
The werebear and werewolf builds, while powerful do have trouble on the defensive end (wolf) or slow attack speed (bear). This makes them a little more difficult than the above characters to play, but not absurdly so. Along with this is their item dependence, especially for weapons. However they do make up for it with increased life pool and insane attack speed/leech (wolf) or
Probably his easiest build would be an Immortal King WWer. Not the easiest set to finish but very viable to solo the game. He's not the fastest character and will encounter trouble when fighting mana burn monsters, or when simply swarmed since he has zero blocking abilities (2-handed weapon). He doesn't have a summonable tank to help relieve the pressure nor any extremely good crowd control skills. A couple of the warcries help, such as Howl, but this character relies on his fighting abilities to win more than anything else.
Concentration barbarians do require a mention. For those that are having trouble finding the entire Immortal King set they make a decent backup build. It is a melee build so a good weapon is necessary, but that is the extent of his item dependence.