I'm hoping to visit both of these castles, but if I only have time for one, does anyone have any advice? Thanks. (I will be visiting as a day trip from London.)

My opinion. Leeds is not a castle as such. More like a manor. The grounds is what makes it a nice visit. For a proper castle Warick will fit the bill.

what time of year? what are you interested in? by yourself or with others/kids?

Warwick is an all-year-round place, lots to do indoors, rich with history in a slightly Disney-fied way. Leeds is a beautiful building in a gorgeous setting, but only in decent weather. nothing much there besides the gardens. the countryside is lovely too, but awful in the rain. it's a lot closer to London than Warwick is, so if it was washed out, you could go back.

Leeds Castle isn't even in the top 15 castles in Kent let alone in England. It does have lovely grounds -- but the castle itself is more of a wedding/conference venue. There is absolutely no comparison between the two. Leeds is 'popular' mostly because of the massive marketing they do.

Any reason those are your only choices? Warwick is definitely the 'better' castle of the two -- but there are many other terrific castles in south and southeast England.

Warwick - no question

Our children loved Warwick and trust me - we dragged then around all English Heritage sites.