Its really not sure, both way have their own disadvantages.
I will say never park your bike anywhere, where there is a chance of you losing its sight, whether busy or quite place.
When you have to be permanently out for several hours, then
- Find a good secured parking spot to park your bikes.
There should be a guard around or someone who is responsible.
- make sure he knows you have parked a bike.
- Or, you can also ask him to keep an eye on the bike (depending on the nature of the person)
If its possible, make irregular visits to the parking spot. Confusing the thief.
- Complete your work and rush to your bike :)
At my city, I park around a firm thing. Whether poles, or railing, to increase the difficulty (but its not allowed everywhere, so not so helpful).