I had an Aquatica housing for the Coolpix995 and was quite disappointed. They have fixed all their little design flaws on the A5000. It is definitely a solid design. The housing now allows use of the TTL meter and eliminated the 45% angle and has a small shroud over the LCD screen for easier viewing.
The Ikelite unit, like all Ikelite units, is solidly designed and constructed, albeit from plastic as opposed to aluminum. I haven't found the plastic to be an issue versus aluminum, although aluminum will be stronger in case you use your housing as basketball. The suggested list price of the Aquatica is only $100 more, so it's a tough choice. Also, if you go Ikelite, you will need an Ike to Nikonos synch cord. With Aquatica, it's Nikonos to Nikonos, so you already own the right synch cord. Ikelite connectors are superior to Nikonos connectors in quality if that means anything to you.
The Ikelite is a little bulkier as usual, but we're talking about a digicam anyway, so in the grand scheme of things, it's small. Ikelite comes with the standard double handle system, superior to the cheap handle on the A5000. You would probably buy a optional tray to use your strobes on the Aquatica.
I don't think you would disappointed one bit with either housing. I also believe that this is the best digital "prosumer" model for underwater use because of its macro capability and TTL compatibility.
I'm not familiar with the L&M, except that it is $500 more.
E-mail me for a quote on the A5000 or Ike.