What game have you played the most?

The hours involved at BL 1 was for playing as all 4 characters, as they have different "action skills".
However, what you said about Borderlands 1 getting boring was kinda due to the limited loot pool that was actually good. what did it in though for me was a glitch from a feature not fully implemented that caused a bug: the Weapon Proficiency actually caused you held gun of the same type to DOWNGRADE itself when in a weapon slot (i.e. a level 69 SMG on a character with SMG Proficiency of 40 actually worked like a level 67 SMG...two levels below).

Borderlands 2 on the other hand gives much more distinction between the weapon manufacturers. A run-down of each manufacturer:

Dahl: Semi-auto pistols and slower automatic fire on other weapons when aiming from the hip. All weapons do burst-fire when aiming down sights. Shields drop shield booster pods when hit. Dahl makes "Bouncing Betty" grenades, which start bouncing and shooting bullets in 360 degrees upon detonation.

Torgue: All weapons deal explosive damage exclusively. In addition, bullets fired from these guns travel slower. Shields from Torgue are strictly Explosive Spike (damage dealt when meleed) and Nova (damage dealt when depleted, shield must fully recharge before another nova can go off. Makes "MIRV" grenades which explode into child grenades that explode for the same amount of damage as the original explosion.

Maliwan: Weapons have higher elemental damage and chance for damage-over-time effects. Spike and Nova shields are available in all elements except Explosive. Maliwan makes "transfusion" grenades which crates child grenades which home in on an enemy and steals health from them to give to you.

Tediore: Weapons are tossed and explode like grenades upon reloading. If reloading with ammo still in the magazine, the remaining ammo is used up but the reload deals more damage. Tediore shields are the only ones with no special effects, but have a higher recharge rate and lower recharge delay than the other manufacturers. Grenades are standard explosive grenades that deal damage based on its level.

Hyperion: Weapons have a lower initial accuracy, but quickly become almost 100% accurate for as long as you pull the trigger. Sniper rifles have a bit of sway to start, but become more accurate the longer you aim down sights. Hyperion produces "Amp" shields, which increases the damage of a shot when it is fully charged at the cost of a bit of the shield draining to amplify the damage. Grenades are of the "Singularity" type, which IMPLODES and pulls in enemies before exploding later.

Jacobs: Normally non-elemental (only 4 elemental weapons exist as "unique" weapons), all Jacobs weapons are semi-automatic. They, however, fire as fast as you can pull the trigger for all but their sniper rifles. They sport the greatest overall damage to compensate for non-elemental status. Jacobs does not make shields or grenade mods.

Vladof: Slightly lower damage than mist weapons, but they make up for it with the second largest magazine size of all weapons manufacturers and the highest fire rates. Vladof rocket launchers have a gimmick where each third rocket fired does not cost rocket ammunition. Vladof makes the "Absorb" shield variant, where there is a percentage chance when the shield is hit that it will negate the damage AND transfer the ammo to your ammo backpack. Vladof makes the "chemical sprayer" variety of grenade mods which varies depending on the element (fire creates a revolving flame jet, corrosive creates a corrosive cloud and shock creates a "tesla coil").

Bandit: Weapons have middling to poor damage, and are not as accurate as other manufacturers. However, they they do have the largest magazine size overall, but have a slow reload time because of it. Rocket launchers made by the Bandits fire 3 rockets at the same time for the price of one. Bandits make the "Maylay" shield, which boosts melee damage dealt to your enemies when depleted. Bandits also make their own versions of the "Bouncing Betty" and "MIRV" grenades.

Anshin: Only makes shields of the "Adaptive" variety. In essence, you gain resistance to the last elemental damage that hit it as well as gain a health boost when wearing it.

Pangolin: Another shield-only manufacturer, they make the "Turtle" shield. It basically has a much higher shield capacity at the cost of a certain amount of your maximum health.