The best place to level is in a multiplayer game where you are partied with people near your level, or not partied with everyone else higher level and on a different act. Then make sure that the monsters you are fighting are within +/- 5 levels of yours if you are < level 25.
A good way to level up quickly and in which you will find an entertaining challenge is to start a normal game and call it something like "Act 1-3 normal". Once 4 or 5 higher level characters have started off into Act 2, you are set. I sometimes do this repeatedly finding beasts my level just to maximize my level before Act 2. Starting Act 2 around level 14 - 16 is what I aim for. I try to start Act III around level 20 - 21, and Act IV in the high 20's. If you are playing hardcore you would want to keep a higher margin for safety. Some character classes like necromancer are easier if you can wait to face Diablo after level 30, where you can use your most powerful skills.
I find Act V is easier than Act IV, and experience is laying around in huge puddles. 3-4 repeats of Glacial trail, or Bloody foothills moves you quickly to the higher levels. Act V normal monsters are between levels 40 and 60, and you are unable to complete the Ancients before level 20. I've never faced the Normal Ancients, less than level 30 as I tend to sweep all monsters from every level if a most methodical and grueling manner. :)
There are some pretty good experience calculators around that will tell you which monsters are perfect for your level, and where to find them. Otherwise, consult the Arreat Summit monster guide to find which monsters yield the most experience. After lvl 25, you just need to find areas with many monsters higher level than you that you can kill quickly.
A good way to level up quickly and in which you will find an entertaining challenge is to start a normal game and call it something like "Act 1-3 normal". Once 4 or 5 higher level characters have started off into Act 2, you are set. I sometimes do this repeatedly finding beasts my level just to maximize my level before Act 2. Starting Act 2 around level 14 - 16 is what I aim for. I try to start Act III around level 20 - 21, and Act IV in the high 20's. If you are playing hardcore you would want to keep a higher margin for safety. Some character classes like necromancer are easier if you can wait to face Diablo after level 30, where you can use your most powerful skills.
I find Act V is easier than Act IV, and experience is laying around in huge puddles. 3-4 repeats of Glacial trail, or Bloody foothills moves you quickly to the higher levels. Act V normal monsters are between levels 40 and 60, and you are unable to complete the Ancients before level 20. I've never faced the Normal Ancients, less than level 30 as I tend to sweep all monsters from every level if a most methodical and grueling manner. :)
There are some pretty good experience calculators around that will tell you which monsters are perfect for your level, and where to find them. Otherwise, consult the Arreat Summit monster guide to find which monsters yield the most experience. After lvl 25, you just need to find areas with many monsters higher level than you that you can kill quickly.