I prefer to book flexible, pay at hotel rates 99% of the time, so if it's last minute and I know plans won't change, HotelTonight works very well (it was really great when founders card offered a 15% rebate for a few years...that's gone and so is my founders card!). I've found the in-app concierge to be helpful in making special requests of the hotel as well.

I have used priceline and hotwire for last minute too, especially when I have time to decode the hotel name--I dislike the deceptive costs buried in the "taxes and fees" these sites now have (Hotwire's are particularly high).

If I have time for a process, I usually start using Kayak (always sort using: nightly rate, including taxes and fees) to get an overview of relative pricing. Also orbitz can be good, since there are always app-only deals and often codes for 10-15% off certain hotels.

Again, I hate prepaid rates, so usually just end up booking BAR in the GDS or direct with chain website using one of the affiliate codes I've (ethically) accumulated over the years. Sadly, materially discounted "travel agent" rates are largely a thing of the past...