well I want a Marshall and have a couple of fenders already (princeton reverb and a twin reverb).
I want it to sound different (not that i don't love my fenders...i do), I want the master volume and effects loops for some variety, and give me something unique to my above amps. Not in the market immediately but maybe sometime next year. Now just trying to educate myself.
The DSL will give you a wider range of gain level... everything from dirty clean to over the top gain... lots of guys use the origin as a pedal amp.. takes a pedal to coax some real Marshall dirt out of it without having the volume on full.
I have the DSL 40c so my vote would go to the DSL. Now the 40 has some nice cleans as well, but since you have the Fenders I would play them looking at the crunch to high gain to see which amp you think suits you best.
Being mostly a Fender guy, my first foray into Marshall ownership is an Origin 20C.
I've played other people's DSLs, but never had the chance to really sit and tweak them. That being the case, I've never fully warmed to the DSLs, either. But, the first time I plugged into an Origin, I knew I'd own one. I like the old school, JTM45 vibe.
I've used mine for relatively quiet practice at home, band practices and gigs and it's performed well in every scenario. I do use pedals for additional dirt, but I use them with all of my amps.
I must also admit that I do not care for more modern sounds, I'm a tweed kinda guy. My other amps are a '58 Twin, a '59 Bassman Ri, a Cox Ultimate 5e3 and a '63 Vibroverb Ri. The Origin fits right in.