Surprisingly, I think the best one in Singapore is from Four Leaves, a bakery chain with a store in almost every major shopping mall. The cream is light and slightly sweet and the sponge cake is nice and fluffy. Most importantly, it's available in almost every mall so it's easy to get your hands on one.
Tampopo Deli (at Liang Court) also sell a very good one. I like their strawberry shortcake and Scoop Cake. Some think they sell the best strawberry shortcakes in Singapore. I think their cream, which is milky yet light, is indeed nicer than most other places.
Patisserie Glace (at Icon) also makes a pretty good one. It's one of their best sellers and the cake indeed looks very pretty. The plus side about their strawberry shortcake is that they don't stinge on the strawberries. But I find the cake a tad too moist and hence not as fluffy as I'd like it to be.
If you know of any fabulous strawberry shortcakes, do let me know!
Four Leaves' creation
From Patisserie Glace