I'd say the chocolate ones are the worst - what have you got by 20th Dec - a cardboard box with open doors and lots of lumpy plastic empty holes - not even a range of pretty Christmas pictures or a Christmas scene to look at - just a scraggy, torn, box. Isn't an adven calendar meant to be a decoration - but a chocolate one, once even partly opened looks horrible.
Personally I'd go for a picture one (prob re used each year) or maybe a reusable one. Playmobil strikes me as reusable and decent, but some of the ones with crappy toys or stationary like Smiggle or TInc are a bit of a waste of time. That said, it's surprising how much pleasure a bit of plastic crap can give a small child every day for a whole month - often more than an expensive toy on Christmas Day.
I'd say that if your child would really enjoy a piece of tat each day,Nathan get a toy advent calendar and reduce the Christmas present spend accordingly.....but don't bother with the horrible chocolate ones, unless you've got one that you fill yourself with sweets and leaves a decoration behind.