It's all about old Pindle ;) . If you have the red portal, you can access his area directly from town, making him nearer even than Mephy. If you have just the WP, you have to go up two levels, and then you're behind him instead of in front. So it's not as good strategically and it takes a lot longer.

Pindle doesn't have the best drops in the game (I'm sure that'd be Mephy), but he does have the best possible drops. Mephy can't drop some of the elite items, and there are some items even Baal can't drop. However, AFAIK, Pindle does have at least some chance of dropping any set or unique item.

And he's a normal monster, so you can use find item on him ;) .