I've personally owned 3 boats before and have been around dozens of other boats in my 30 or so years of boating, of which I currently own a 2004 Grady White 228 Seafarer as well as a 2009 aluminum I beam bunk trailer. During those 30 years, I've owned and/or used both roller as well as bunk trailers and I personally prefer bunks as well as an aluminum trailer. The reasons are many but to name a few... the aluminum isn't going to rust like a galvanized steel trailer will and it'll be lighter as well as easier to tow. Bunks are also easier and cheaper to replace as opposed to having to purchase each individual roller when the time comes around to replace them. Bunks will also if setup correctly distribute the weight a bit more evenly as well, compared to rollers that have a lot of weight sitting on a small roller and can leave indentations in your hull. I personally think that bunks are easier to launch and retrieve, and as others have mentioned you typically don't have the worry of the boat rolling off the trailer on a bunk trailer.
My previous boats were two 21' Arima's and one of the guys on the Arima owners forum actually bought a brand new roller trailer, of which the boat rolled off the trailer at the ramp, landing on the concrete. He did undo the safety chain prior to the boat being in the water, but contrary to what has been said, winches can break or slip as well as the safety chains, they can rust, corrode and so forth. I'd rather just not have the concern of having a roller trailer, especially if you've got the choice and you can avoid it. Lastly, with regards to the weight... listen to what luckydude, myself and those that have actually have/had 228 Seafarer's say as opposed to others who haven't and are talking about dry weights as well as just guessing on numbers. Get 3,500 lb axles and nothing less than that as 6k lbs isn't likely going to be enough considering that my boat alone was 5,300 lbs on the scale. And that was with only a half a tank of fuel, no water, minimal gear of two downriggers and two fishing poles, next to no other gear or bait or food/beverages etc. If you have a full tank of fuel and your boat has an auxiliary fuel tank that is full or partially filled, along with a good deal of gear, a bait tank, water tank full, food, ice, etc... then you're going to be well over that 6k lb rating. Definitely not worth the potential risk just to save a few bucks and very much one of those situations where a bit of overkill is a good thing.