Having had both (a few times), I'll give you my take on these.
For a heavy boat @ shallow ramps you can't beat a roller IMHO. Even at steeper ramps they are slick. Much more to the maintenance and upkeep plus expensive. All pivots must remain loose and the rollers need to be well lubed to last. Something many don't like is the fact that when loading you can't "stick" the boat part way on (because it'll roll right off again if maintained properly). What I do is drive part way on and leave it idling in gear until hooked up and the slack is removed. Works good for me on what I believe to be a 3500#(ish) Parker. Deep "V" helps to keep things centered very well.
For lighter boats where you can (at least) almost float / power off I'd really prefer a bunk trailer. They do support the hull better generally. Much less to the maintenance and usually lower (hull to road) which helps at the launch. Some folks have a hell of a time getting them setup correctly (don't know why). I feel they are definitely the way to go on semi-V or flat transom bottomed hulls. "Guides" on the rear of the trailer will put it right where you want it.
I'd recommend a w-i-d-e self centering roller on the rear of the trailer, especially if you're intending to drive onto it in windy / tidal conditions.
Simply get the bow stuck to the wide roller, line it up and drive straight on (GENTLY! no Rambo stuff needed).
I love the bunk trailers for lighter boats,,, but not for heavies.
For you -
I'd strongly recommend you consider a bunk style with keel rollers for your aluminum hulled boat. Mainly for the support the bunks offer.
You'll want it set up so 1/3 to 1/2
the weight of the boat is always resting on the rollers. Makes loading /launching a bit easier, plus the keel will be the strongest point on the hull for taking those potholes on the hi-way. The bunks will be much kinder to your rivets, welds, and thin aluminum. During storage (if left on the trailer) you'll be less likely to put a "set" in the hull like you'd probably would do with a roller trailer and no keel rollers for keel support.
Definitely have the trailer set-up with some of the bunk showing behind the boat for transom / motor support,, only 1/4" is good, more than a inch isn't necessary though.
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