i have 2 dwarf hamsters, they r gr8, they are easy to keep as well as cheap they love to be petted but they dont need loads of attension. we have 2 because they are very social. i love them!!! defo recommend them
Guinea pigs are amazing - although they don't NEED to graze outdoors, the joy on their wee faces when they do is quite something... so I think I'd feel bad about depriving them of that luxury! They thrive living indoors all year round otherwise. Maybe you have a family member or friend who could supply a nice lawn for them to visit a few days a year?
I've had 1 male Guinea Pig (entire if anyone wonders), several male Hamsters (Syrian, and of course not in the same cage) and 1 male Siberian hamster, as far as I can recall, neither they nor their cages smelled much more than the females/the female's cages, so I don't think that they have to be smellier to own.
About being able to take Guinea pigs outdoors, if they only live indoors, they won't know anything else exists. If the owner still worries about them missing out on something, as suggested by Cloverleaf1985, you can always buy some seeds (wheatgrass, Sweet Oats or maybe something else?), and grow them in one or more little pots or trays in a window.