I was KKH B2 for my second and honestly the experience really depends on which ward you get, so it's quite a lottery. My stay was smooth, nurses were helpful, and yes there's aircon in the B2 wards these days, though some rooms are a bit snug. For normal delivery I was discharged on day 2, which is pretty standard unless there are complications.
That said, a few mums I know switched from KKH to SGH B2 and didn't see a massive difference in care quality, just different systems and waiting times. Since you're already under KKH and they have your medical history, I'd say unless you have a specific concern, switching midway through your pregnancy might add more hassle than it's worth. But if the reviews you're reading are from recent months and they're giving you real pause, it might be worth a consultation call to your current gynae to ask what to expect this time round.