I think the advice to look for chromoly steel only is a bit dubious. We have been riding Aluminium-framed, mass production bikes for several decades now and they work fine. There is nothing wrong with chromoly frames (I have 2) but I also ride an Aluminium frame.
Since you are a big rider , 6'3", 225 lbs, you need a BIG FRAME. The largest "size" available is usually 23" but the exact fit of a 23" frame really depends on the length of the horizontal top tube (TT) rather than its standover height.
Trek FX (25" size) quote a TT length =60.3cm
Cannondale Quick (jumbo 23") quote TT length = 62cm.
The Trek "size" is larger but the Cannondale frame is longer so would fit a big rider better. When you go to view a bike, take a tape measure and find out the horizontal length from (centre of) seat-tube to head-tube.
I always like to recommend Cannondale for larger riders, they make some of the largest production frames and the style of their frames is very stiff. Larger frames always suffer from lack of stiffness compared to smaller versions of the same frame so extra stiffness is always welcome. I would never recommend Cannondale for small riders, they are much stiffer than required so not as comfortable.
The hybrid/fitness style of frame is good for general purpose commuting. They come with threaded eyelets for fitting a rear luggage rack and bolt-on fenders. Cannondale also do a very nice touring bike in XXL size that comes highly recommended for longer distances.
Big riders need strong wheels. You can upgrade the wheels but I would look for a conventional 36-spoke design rather than 32 or fewer spokes.
For long commutes, a larger wheel (700c size) found on road/hybrid/touring bikes will roll more easily than the smaller MTB (26") wheel found on so-called "comfort bikes".
The other dimension that is useful for big riders is crank size. Look for a bike with cranks that are 175mm long rather than the medium sized 170mm. You dont find any longer cranks on production bikes. Long legs can pedal more efficiently on long cranks.