You can use whatever fruit you like but my preference is for either plums (which is how I first experienced it), or pear halves with some form of berry/cherry (raspberry, blueberry, or sour cherry).
For simplicity and speed I use tinned fruit (this is usually a cake I make when I don't have time to throw together anything else but want to offer something lovely and fresh from the oven), and whilst I love plums or pears many people I know will use peach or apricot halves too. It is important that you allow the fruit to drain on kitchen paper first whilst you get the batter ingredients together. And if you are using frozen berries/cherries take them out of the freezer first 30 minutes before baking to take some of the chill off them.
I also ensure that when using plums I remove the pip ... whilst not many people worry about this I don't want to risk anyone losing a tooth (or two) by accidentally biting onto one ... to do this I use a small sharp knife and cut through the natural slit in the plum and slowly use my knife to dislodge the pip. It may be that the plum will fall apart a little but I keep it together and still use it, as once its in the batter that holds it together. The other option is to cut the plum in half anyway and use more of them to scatter over the batter ... but I like to keep them whole placing them strategically around the cake.
Whilst the cake is baking the fruit you have used will drop to the bottom, so when you turn it out upside down onto your serving platter the fruit will be showing. A light dusting of cinnamon sugar finishes it off and I can tell you honestly it is superb. Everyone will love it. Promise!
NB: I use a combination of raw caster sugar and ground cinnamon for the cinnamon sugar ... I have a "dusting" dispenser of it always on hand in the pantry. To make fill ⅔'rd of the container with sugar, then add a teaspoon of cinnamon at a time mixing it in until you have the strength you like (I love it with heavily scented cinnamon). So stop once you like the look of it, and can smell the strength of the cinnamon in it.