I decided to try my hand at optimizing some Guildhall combos.
Beggar + GuildhallThis can be insanely fast, but it's very inconsistent; if your Beggars clump together, you lose a lot of turns. My strategy was to always get three Beggars and Guildhall in the first 4 turns. Buy Provinces when possible. Buy additional Beggars on turns 5-7 if you miss Province. After that, buy Silvers instead.
Turn 8-12: 4 Provinces, ~27 VP
Turn 10-14: 6 Provinces, ~39 VP
Turn 13-17: 8 Provinces, ~51 VP
Delve + GuildhallThis combo is pretty comparable with Masterpiece, but with slightly higher highs and lower lows. My strategy is to buy Guildhall ASAP (a 2/5 or 5/2 is great). Pre-Guildhall, just Delve as much as possible. Post-Guildhall, use a Coffers if you have an odd amount of money, buy as many Delves as you can, plus a Copper. Green starting on turn 6 if you have an amazing start, turn 7 usually, and turn 8 if you have a weaker start (often caused by Guildhall on turn 4+). If you get $9 or $10 naturally, you can Delve + Province.
Turn 9-11: 4 Provinces, ~27 VP
Turn 12-13: 6 Provinces, ~39 VP
Turn 15-16: 8 Provinces, ~51 VP
Masterpiece + GuildhallThis strategy is the most reliable to 8 Provinces, but the slowest to 4 Provinces. I just buy Silvers pre-Guildhall. Post-Guildhall, use all your Coffers and get the biggest Masterpiece overpay you can! Green starting on turn 7 if you have ~15+ Silvers. Green starting on turn 8 otherwise.
Turn 10-11: 4 Provinces, ~27 VP
Turn 12-13: 6 Provinces, ~39 VP
Turn 14-15: 8 Provinces, ~51 VP
So, these are all really strong! Monolithic Guildhall strategies are also worth looking out for with Banquet and Cache (and maybe other cards I'm not thinking of).
Edit: Banquet + Guildhall is also very strong. The baseline Banquet for Silver isn't as strong as the above, but it isn't hard to find something on the board that helps. A better treasure (or treasure gainer) helps, as does +buy. I got 8 Provinces in 13 turns with Banquet +
Spices + Guildhall.
Counterfeit and
Charm were strong. I expect
Treasure Trove is also great.