I dislike the Sl 120 standard. My characters always seem to reach their optimal level at around 50-60, and past that I just seem to end up pumping a bunch of levels into Vitality and Endurance, which tends to make the build more generic.
I prefer the diversity and the sacrifices you have to make at lower levels. Want to max magic damage? Okay, but you won't be able to tank hits. Want to wear the best armour but maintain mobility? Sure, have fun with your elemental weapons and lack of magic. Jack of all trades? Fine, but don't run off crying when you get beaten up by someone with a more focused build.
Of course, you could argue that having a high level generic build allows you to explore a greater variety of techniques and equipment than a more limited low level build, but I prefer having several unique characters at low levels to one high level character.
It probably has to do with the fact that I can complete a low level build, including a maxed out weapon, shortly after I get the Lordvessel, but getting a character to 120 usually requires me to go a decent ways into NG+ or do some boring grinding. I also like the early areas more than later ones like Izalith and New Londo.
It also comes down to what type of PvP you prefer. If you prefer organized dueling then 100-120 is obviously going to have the most action for you, but for invading you'll want to stay at a level appropriate for the area. Also, darkwraiths and people using the red soapstone can invade/be summoned by anyone with a higher level than them while only invading down by (10 + %10 their SL) levels, so a Sl 1 red phantom will have the most potential PvP action, decreasing as levels are gained.
I also wish that Gravelord phantoms would show up in NG. While it might be unfair for new players, it would certainly make things more interesting for experienced players, not to mention the Gravelords, who are far too rare as things stand.