Welcome aboard Jackaljay, the
real critical difference is that the Om150 is
flat backed, braced solid wood:
guildguitars.com
That's discontinued BTW so I'd expect to see some deep discounting there.
The 250 is
arched back, laminated, no bracing:
Guild’s signature arched back design allows for great volume and projection, long sustain, and a lush, full sound.
guildguitars.com
There are subtle voice differences between the 2, as I took years to discover between my own D25 and D40, which are essentially same build formula except for back configuration.
In my opinion an arched back is better for a pure strummer, makes chords sound "fuller", but in my case at least, the D40
records better, with the least distortion. And for strumming, it's more "focused", one can hear individual strings more clearly. I'd expect similar qualities to apply to the OM-150/250 comparison.