Malmö

Looks like Malmo got pretty well slammed in this thread:
https://community.ricksteves.com/travel-forum/general-europe/advice-for-a-solo-traveler-malmo-vs-strasbourg

I'm not sure the people in that thread really "slammed" Malmö so much as pointed out that Strasbourg was by far a better match for that particular poster's interests (especially since they were looking at spending a full week there). Likewise here - if you're interested in seeing "sights," there are certainly more of those in Copenhagen. But for a short stop, with a free hotel room in the mix, Malmö could still make sense.

How much time for sightseeing will you actually have? Unless your flight from England is early in the morning and your flight home the next day is late in the afternoon, it might not be very much.

I think another thing to consider is that the railway tickets appear to be about $15 per person each way. So that "free" hotel will cost you about $60 to get to and from. That is if "we" means two people.

I thought about mentioning that. But the train from Copenhagen airport to Copenhagen city center costs around $5 each way, which negates part of the difference. So assuming a party of two, it costs about $40 more in train fares to get to Malmö to use the free hotel night. There's no way you can get a hotel room in Copenhagen for anywhere close to $40, so they'd definitely be saving money by going to Malmö (assuming that the free hotel certificate really is free and doesn't load you down with a bunch of nonsense fees just to use it).

We visited Copenhagen in 2014 and heard about problems in Malmo, which is close to Copenhagen.

This is something I found on the internet about Malmo.
https://www.rt.com/news/310757-sweden-malmo-blasts-crime/

Thanks all for the replies. As a follow up to a few inquiries, yes, the hotel is fully free, including taxes. Also, I failed to mention we land in Copenhagen at approximately 430PM and our return flight home is at noon the following day. So, that does not leave a lot of time for sightseeing but provides plenty of time to get to the airport the next day. So, really, we are looking at about 6 hours of sightseeing for the two of us. Not to do a full redirect, but I did see a few things online suggesting Lund as a easy and enjoyable day trip from Malmö. Any thoughts on Lund? With limited time, I am leaning to just spending it in Malmö but, again, open to suggestions. Thanks.

Also, I failed to mention we land in Copenhagen at approximately 430PM and our return flight home is at noon the following day.

Hey I take chances all the time, but I fail to see how much sight seeing is actually going to take place. I am assuming you will have your large luggage checked through when you leave the UK, so will just have over-night bags for carry on. So let me walk through this.
Land at 4:30 pm
Off the plane, clear immigration and walk to the train station 5:00 pm
Buy the train ticket and get your passports checked again to go to Sweden wait for the next train, 5:30 pm
Train ride to Malmo 6:00 pm
Get off the train and walk 1/4 mile to the Marriott and check in, 6:30 pm
So now you have time for dinner and sample the night life of Malmo.

Now working backwards from your departure at noon
Be at the gate at 1 hour before flight for special security for International flights to the U.S. 11:00 am
Be at the airport to get through standard security and passport control. 10:00 am
Get off the train from Malmo, 9:45 am
Board the train in Malmo, 9:15 am
Be at the Malmo station, 9:00 am
Leave the Marriott and walk to the station. 8:45 am
Be in the lobby to check out of the hotel 8:30 am

So it looks to me like 6:30 pm to 8:30 am the next day to "sight see". When are you going to sleep?

I don't know if this thread is still of use to the OP, but in case it's relevant to anyone else: I was in Malmo earlier today and I can confirm that it's very possible to pass several pleasant hours in the place, just walking around the pedestrianized downtown and looking at the shops, buildings, and people, listening to the buskers, and watching people go about their daily life in an environment that, while bustling and vibrant, isn't meant to cater to those tourists who think of Europe as a continent-sized amusement park. The shops all close around 7 pm, so the atmosphere may be different in the evening, however. Also, there are public toilets - for example, in the Triangle shopping center - that don't require coins.

As for "attractions," there was a boat tour of the canals/rivers (daytime hours only) that looked like a lot of fun. I decided to skip it, though, so I could get to Copenhagen in time for dinner.

Thanks, appreciate that as we will be heading there in a couple of days.