Thanks folks!
- based on your recommendations I ruled SQ out...
Almost about to book BR but then, in the process of re-confirming the prices, NH also popped up (didn't realise they had a Premium Economy too).
Couldn't find a way to check window seat availability on the BR website before booking, and given a soon-ish departure date didn't want to take the risk of a middle seat.
BR had a 5 hour transit in TPE which sounded enough to get out of the airport, but the connection was in the evening, so I figured not much would be open.
On NH I got 8 hours, from 8am to 5pm - enough time to get the express train into town and back.
Also now routing to SJC and back from SFO to add a little extra variety too.
Will look back at BR when I plan a trip to Taiwan.