Proposal

The cliffs on the hill behind the big house in Strangerville! I know its an odd town, but the views from that little cliff-side park is beautiful. Also, if feels fairly secluded. I've seen very few sims up there so there shouldn't be any unwanted interruptions.

Did they ever fix that bug where proposals outside were automatically rejected? Wherever you do it, better save your game first just in case.

The bluffs in Windenburg during a lovely warm summers day, in the open rural setting in Windenburg during a lovely warm summers day. In San Myshuno Meadows in front of the wedding arch!, also during a nice warm bright day out. Willow Creek Park or behind the four community lots in Willow Creek as close to the lake as possible. There are plenty of romantic and picturesque spots around.

During some autonomy and a bit of luck i've seen proposals on the porch of Garden Essence (BFF household), and inside that house in Liberty Lee's room at the back. it's mostly just right timing and the types of mood they are in as well. But yes, always save before hand when you do pop the question as even with the right mood and setting it can be rejected even so (and in some cases it is very strange to do so, especially given the context).

That big garden estate with the maze in Windenberg is super beautiful! Or in Sulani on one of the beaches at sunset.