There are a few things to consider when deciding what to provide for guests to sleep on. The most important factor is probably comfort, followed by budget and then space.
Assuming that comfort is the priority, there are a few different options available.Air mattresses are generally quite comfortable and relatively inexpensive. However, they can be bulky and take up a lot of space, which may not be ideal if you have limited space in your home or apartment.
Futon mattresses are also quite comfortable and reasonably priced. They tend to be smaller and more compact than air mattresses, making them a good option if space is tight. Futons can also double as seating during the day, which is an added bonus.
If you have the budget for it, investing in a nice guest room set (including a bed) is always an option worth considering. This will obviously take up more space but it will also provide your guests with their own private retreat during their stay with you - something that many people appreciate.
In terms of specific products, there are plenty of options out there depending on your needs and preferences. Do some research online or ask around at your local furniture or bedding store for recommendations.