My views of the lounges are somewhat biased since it usually includes the breakfast experience at the restaurant. The river view from the LM flanked by the bridge could arguably be better than the Vinpearl except Vinperal has a much grander and panoramic view of the city.
What makes LM above average for me is that I truly enjoyed the view from the window seat during breakfast at the restaurant. You are far enough away so the constant street beeping is muted, but yet close enough to be constantly amazed by the constant stream of scooters. It seems chaotic but yet super efficient.

Vinpearl has the grander view (being the tallest building in Vietnam) and with lots more food choices. You have the usual freshly squeezed juices/smoothies and omelette station but I also enjoyed the freshly made Pho and Bánh Cuốn.