I'll go "chronologically" -
Second, BG1. Honestly, if you feel it's better than Pillars, I have to think you have some major nostalgia goggles on.
I played BG1 after PoE, so no nostalgia goggles here. My first IE game, however, was PS:T, I played it before PoE, but I wasn't comparing the two at all.
Aesthetically Pillars is a clear win -- BG1 is functional but pretty crude. Just take some screenshots and look at them side by side. Do you really prefer BG1?
BG is more aesthetically complete, it has a coherent art direction for everything. The honestly cruel-to-the-eyes 3D models of Pillars are horrendous. In terms of creativity both are forests and generic towns, but BG1 has more things to see - the statue of Ellessime, the big cathedral of Lathander in Beregost, Beregost itself being more of a living town than any in Pillars, the lakes and waterfalls are more like lakes and waterfalls than the spoon-big ones in PoE, Nashkel's carnival, the different districts of Baldur's Gate have more character than anything in DB or Twin Elms. Maybe these are my preference, but I don't think anyone can say that PoE has a unified art direction with those 3D models.
BG1 dungeons are, for the most part, pretty primitive. They're mazes of narrow corridors mostly filled with kobolds. Or, later on, other beasties. Repetitive mobs in any case. Durlag's Tower is good, but it's not in the base game -- and WM is a much bigger, better integrated, more beautiful, and more challenging experience than TotSC.
Firewine Bridge and Ulcaster's School are pretty primitive, yes, the Thieves' Maze is horrendous. The dungeons in base PoE are just as shit, so whatever, Eothas' temple is just rooms after rooms. Od Nua is a horrible experience. Yes, BG1 doesn't have anything resembling Raedric's Hold, but PoE doesn't have anything resembling Durlag's Tower.
BG1 companions are sparsely written and pretty thin gruel compared to Pillars'. They do have quests, but these are simple, straightforward affairs. They don't have much dialogue, and there's barely any intra-party banter (if indeed there is any at all). Honestly, is Kivan more interesting than Sagani? Dynaheir than Aloth? Minsc than Edér?
I wouldn't say Sagani, Aloth and Eder are
interesting at all. They just interrupt the flow and whine and bitch, and moan throughout the whole experience. If we are comparing only PoE and BG1, I prefer BG1's very sparsely written ones. That may just be a preference, but if we compare Kotor 2's to both BG1 and PoE's, I'd prefer Kotor's.
BG1 quests are, again for the most part, straightforward go-there-do-that. Some are straight-up bring-me-umpteen-bandit-topknots. Pillars' aren't the best in the world either, but there is a lot more to most of them than that.
Both BG's and PoE's are on the same level of interest, but at least BG1 doesn't suffocate you with lore dumps with each one. Just 2-3 sentences and that's it. Much prefer BG1's in this regard.
BG1 maps are, for the most part, pretty empty. Most of what you can do there is grind mobs for XP and find the occasional treasure.
They are big and it makes the experience big and vast, it creates breathing room and symbolizes the bigness of the forest, even if they are somewhat empty. PoE also has a lack of quests and interesting things to see in the maps, but they are much more samey than BG1's.
With character- and party-building, Pillars wins hands down. AD&D from levels 1-8 or so is very, very thin gruel compared to the Pillars classes from 1-12, or 16 if you include the expansions.
Yes, PoE has more character-building options, but I have more fun playing BG1's classes because they offer a type of variety that PoE doesn't. I can't really explain why atm, it's more of a contextual thing than an isolated bubble. I already mentioned that PoE's variety comes from archetypes rather than classes. Melee DPS, Ranged DPS, Tank, Support.
What, in your view, does BG1 do better than Pillars? 'Cuz honestly, I can't think of a damn thing.
A much more unified, disciplined and restrained construct with plenty of replay value and charm. A complete adventure that doesn't feel like patchwerk. A more creative, joyous and artistic "food for the mind". Yes, most of those things are immaterial and hard to define, but at one point you go into things that can't be verbally explained. It's not about feelings, it's a wholly intellectual categorization, but it's hard to put into words. It also takes into account who I am as a person and what my aesthetic tastes have become over the years.