Okay, so custard is great, but it really makes other desserts.
Crumbles become magnificent with custard, as do sponges, like treacle pudding.
Cake is generally a lame dessert, as it is typically better as company to a tea, or a lunch, or even just a snack.
To choose cake for dessert is usually wasteful as many typical desserts work only as an after-dinner dessert, whereas cake can be eaten whenever.
However, sponges tend to get a pass when they are accompanied by a sauce, like custard or treacle, or are in the form of sticky toffee pudding. Ice-cream can also accompany a sponge/sauce combo.
Ice-cream can come in many qualities. On its own it can be good, but when it has wafers, sauces, possibly chocolates or even fruit with it, it can be on a whole other tier.
Sorbets are harder to dress up, and don't usually need sauces on account of their sharper flavours. They can be boring in style but their flavour is worthwhile.
Meringues are another great instrument, not too appealing on their own, but are a god-send for fruit based dessert.
Pavlovas, a fancy heap of selected fruits (typically berries and grapes) on a whipped cream mattress on a bedframe of meringue are a sophisticated yet delicious dessert.
In a messier and more fun style, Eton Mess makes use of broken meringue, whipped cream, and strawberries, only improving on that summer delight of strawberries and cream, a lovely dessert that during Wimbledon somehow transcends to lunchtime snack.
Meringues also make it into cakes, ice-cream and pies, as the sweet counterbalance in lemon meringue. Besides cake format there is surprisingly little opportunity for lemon, so its presence in a dessert menu is not to be sniffed at.
I think it's impossible to choose a best dessert as any dessert can be fantastic, depending on your mood, your company, the atmosphere and of course what you have already eaten.
For me personally, however, while I may choose others over it, I always have room for custard.