All the BF amps share the same basic topology - front end, tone stack, etc. The Twin and Deluxe have the following differences of interest:
- Twin tone stack as a mid control, the Deluxe does not. This Deluxe tone stack is essentially like a Twin with the mid knob stuck at about 7.
- The Twin has a "Bright" switch, the Deluxe does not.
- The stock Deluxe has a slight treble boost on the reverb/vibrato channel due to a small bypass capacitor on the volume knob. It is like the "Bright" switch on the Twin if it could somehow be turned on half-way.
- The Twin is 80 watts and the Deluxe is 20
Other than that, the reverb and tremolo circuits are identical as is the gain structure. Even the phase splitters are the same, though the Twin runs at a somewhat higher voltage.
The Deluxe can easily be modified to have a somewhat similar tone arrangement. On my '65 DR, I put a push-pull pot in for the Volume control so that I could turn the brightness circuit on and off, for example.
While I love the sound of a good Twin, I personally find amps of that wattage to be total overkill for everything I do. The Deluxe gives me great BF tone at a much more manageable power level, including virtually every electric gig I have had since 1985 - and that's a lot.
So, if you think you will have some really loud gigs by all means get the Twin. If not, I strongly recommend the DR.
I find the DR to be far too much amp in my house, by the way. I can't turn it up past 2.5. For home practicing, I use a BF Champ with a Weber speaker. Add an external reverb pedal and wail away!