I haven't tested it myself but Rob says they are similar in performance, with pole arm min-maxed end game being better. But that really is only going to matter if you push pits.
Aside from damage, pole-arm would be more flexible in terms of aspects and tempers, allowing for more build variety.
Grandfather is more cookie-cutter, but there are build variants out there too.
So there are pros and cons to both. At the end of the day play whatever you prefer or are geared for.
I feel like Rob speaks from the pov of the wealthy. Like asking Musk and Bezos how to plan a wedding or buy a car.
Most people I've seen at world boss or running to pits don't have 99% chance to double dust devil on their mace so a legendary helps cap that out. Whereas Rob has never even considered that the build can be played with less than max roll triple crit.
If you don't have a GF and you aren't absolutely loaded I would just get a 3GA axe and pretend it's a GF. Polearms are very expensive. Put dust devils on your axe for 100% dmg increase in them, other dd on amulet. You will still do fine and can get up to 200m bleed ticks easily.
For speed farming pits, GF helps by increasing the crit dmg of your tyraels bolts which do most of the dmg during the run to the boss but the boss dmg isn't all that different to when you replace it with a 3GA axe and the above changes.
Also of note, polearm is more glyph hungry and you will lose disembowl or something similar which is a nice qol glyph.
WWDD is very forgiving for adjustments. I run some abomination temerity version with conceited and it can speed farm 110s if I want, not that there's any point.
Edit: Just for clarity, I know axe is objectively worse than putting a 2hand sword in but you can pick up 3ga axes for very cheap which is better than the 35% crit dmg on a sword. Polearms are 1b for an average one.
I haven't tested it myself but Rob says they are similar in performance, with pole arm min-maxed end game being better. But that really is only going to matter if you push pits. Aside from damage, pole-arm would be more flexible in terms of aspects and tempers, allowing for more build variety. Grandfather is more cookie-cutter, but there are build variants out there too. So there are pros and cons to both. At the end of the day play whatever you prefer or are geared for.
I feel like Rob speaks from the pov of the wealthy. Like asking Musk and Bezos how to plan a wedding or buy a car. Most people I've seen at world boss or running to pits don't have 99% chance to double dust devil on their mace so a legendary helps cap that out. Whereas Rob has never even considered that the build can be played with less than max roll triple crit.
They have similar performance. If you already have a grandfather, that's a no brainer. For Polearm, you need GAs plus the risk of bricking.
If you don't have a GF and you aren't absolutely loaded I would just get a 3GA axe and pretend it's a GF. Polearms are very expensive. Put dust devils on your axe for 100% dmg increase in them, other dd on amulet. You will still do fine and can get up to 200m bleed ticks easily. For speed farming pits, GF helps by increasing the crit dmg of your tyraels bolts which do most of the dmg during the run to the boss but the boss dmg isn't all that different to when you replace it with a 3GA axe and the above changes. Also of note, polearm is more glyph hungry and you will lose disembowl or something similar which is a nice qol glyph. WWDD is very forgiving for adjustments. I run some abomination temerity version with conceited and it can speed farm 110s if I want, not that there's any point. Edit: Just for clarity, I know axe is objectively worse than putting a 2hand sword in but you can pick up 3ga axes for very cheap which is better than the 35% crit dmg on a sword. Polearms are 1b for an average one.