4d6 is usually where you are dropping the lowest roll.  Still 18 Max.

 

I do point buy as a DM, but most of the time when I play, the DM mandates 4D6 drop the lowest. Sometimes reroll ones if it's not going to be droppd.

 

I preferPoint buy, because, in my experience, anytime 4 people roll random stats, you end up with the following:

1 Super Fantastic Man

2 Average Joes

1 Mr. Retardo

 

I've seen it happen too any times, so in th interest of fairness, I usually do point-buy. I they really want to roll, 3D6, no rerolls, no allocation. Play what you get.

I have an interesting way I like to use for rolling stats.  It lets you adjust your character on the fly and turns stat rolling into a fun game.  The DM can also easily adjust it for power level and it provides for consistant character creation.  Finally it keeps players from having the stereotypical characters. Not every fighter gets their 17-18 assigned to STR,  Dex for rogues, etc  but they can certainly have good stats overall.

Start by writing  the 6 base stats on a sheet of paper  with a bit of space between them.  Then the DM assigns you X amount of dice for rolling stats.  X can be what ever number is fair.  I like to do around 22 for average campaigns, 24 for medium and 28+ for high powered.    Next you take turns picking one of the 6 stats and rolling a D6 for that stat.  You assign that number to the stat and remove that die from the die pool.  Repeat the process with each die choosing to assign it to a stat until the entire pool is empty.   Each stat can have only 3 dice assigned to it, so if you choose to roll another die, it maybe replaces one of the 3 assigned to it if its a better roll.

For example, if you picked a fighter you could start by choosing STR and rolling a D6.  Getting a 4  you set it next to strength.  For the next die you again choose STR and roll a 1.    His current strength is 5.  You then can choose another stat to work on or choose STR again  rolling a 6 giving you a total of 11.   Later on after assigning all your dice you have 2 left and want to improve your strength.   Choosing strength you a roll a 4  and discard the 1 giving you a total of 14.  Finally assigning the last die to STR you roll a 2, and since 4,4, 6 is already higher you just discard the last die.