Professionals are waaaaay better than students, having had both. Out all day, tend to be very respectful of the property, normal hours. Cost less as well, due to said being out more - you have to keep them warm in winter when they're paying you.
DH and I had lodgers before ds arrived, and mostly loved them. One stayed a year and left for work reasons, another two years and bought her own place, and then her best friend moved in and left last October, a month before ds arrived - she was a research scientist, but way past the student phase. They've all stayed friends, and they're all lovely.
My main tip is watch what they do when they visit - do they hang coats up, are they smartly dressed. I'm a scruff bag myself but the one scruffy but fun girl we let move in was a disaster - dropped stuff all over the kitchen and just left it. When we asked her to clear up the bag of rice she'd left everywhere she didn't, and when we asked WTF a few days later over that and various other issues she said she didn't know where the dustpan and brush were, as if that was a perfect excuse (we had two, one in the utility room next to the loo, which she used, and one under the stairs.) The ones who care about their clothes being ironed and cared for will usually feel the same way about your kitchen. Which is my other rule - I decided not to expect any housework from them, just to regard it as a bonus, as long as they didn't actively create or leave mess. That way I was touched and pleased when they hoovered, rather than fuming that they didn't - they were paying the mortgage, after all. It was less aggro to view it like that. And actually one of them did more housework than we did - she was the perfect lodger, in fact. The other thing is we treated them very much as if it was their home that they shared with us. The first totally took the piss (the one we had to ask to leave - she actually had the nerve to ask how many people we were expecting over for my birthday because "I may mind if it's too many") but it was balanced by the fact that the others were scrupulously careful in return. They had dinner parties occasionally, friends over whenever they liked - all we asked was notice so we could vacate the dining room for them if they needed it.
Deposit and rent in advance is vital, IMO, as is checking their employer is legit if you go for the professional option. Also remember that a lodger has far fewer legal rights than a tenant in a house where the owner lives elsewhere. If it isn't working out, you can just ask them to go with a couple of weeks' notice (we gave 6, but that wasn't required).
Tell your insurers - you aren't covered if you don't, and usually all that happens is they insist burglary needs evidence of forced entry. And the rent a room scheme means around 4.5k per annum is untaxed, but you have to pay tax on any more than that. I don't actually know how the Revenue would check, but better safe than sorry.
Those keys that can't be copied are also handy. Most people are lovely - we never had any real trouble - but just in case.