Hoog,
The cradle up front is probably the way to go as the bow is usually the last part of the boat to go under (an air bubble usually ends up in the forepeak) in a 'normal' sinking (allowing for a manual deployment), or a clear shot if it's an automatic deployment (hydrostatic). However, as noted, in really horrendous storms, that's a tough place to ask anyone to go and perform the necessary launching procedures if you go with the manual option.
However, that placement in a rollover/broach would still allow you to have it deploy cleanly, and if it's calm enough, you'd probably be able to reach it to deploy (if the release doesn't work), even if you had to dive to get at it. The negative side of the coin, as you noted, is that it will interfere with your forward visibility if you're running an express/cabin style of boat.
Putting it under the tower supports is risky as there's a real chance that it'll get hung up if it deploys automatically (hydrostatic release) if you roll or go down quickly.
The other option, keeping it down below means that you've got to find space where you can reach it quickly and get the HEAVY and unwieldy container out onto the deck in a rush (sometimes not possible with an engine room fire).
With the many boats that I've run, the bow mount option was the most favored placement for the hard sided rafts on cradles.
The best advice that can be offered is to have the raft serviced annually and hope that it never comes down to using it. However, the simple question of 'How much is your life worth?' is the determining factor when it comes to onboard safety equipment. Don't overlook launching drills with some of your regular crew members as, when the fecal matter hits the fan, you just might be a little busy keeping things together long enough to get the raft ready to go. Also, have a 'sink/grab bag' with all kinds of survival goodies (Handheld flares, GPS, VHF, mirror, strobe, whistle, water, and energy bars) at the ready in an easy to reach place so that if the unexpected occurs, you've got a better chance of both survival and rescue.