I owned both . . .currently I have the 30 combo. Boy, not sure where to begin because I'm using recollection on the 18.
Both had the best FX loops I've used. The 18 was not loud enough for my gig at the time (we had a full-blown Hammond B-3 player).
The 30 seems thicker all the way around to me. The gain on the 30 seems much more Marshally IMO. I like the 30 alot more.
Here's what I posted in another thread about a week ago:
I got mine a few days ago and have been ab'ing it with the 18 trying to decide whether to keep both or sell one. Right now, I'm thinking I'm keeping both. The best way I can describe them now is that the 18 gives a really juicy sound and the 30 gives a beautiful present snappy sound. I've triied them both through a CAA 2x12 with a V30 and a Governor and a Port City 1x12 loaded with a Cele Blue (at low volume so as not to blow the Blue). My overwhelming preference with both of these amps and with all guitars tried is is the Blue. I have a higher wattage Scuminico on the way and that's what I intend on using. My Grosh tele with Fralins is the best sounding guit.
So far, the honeymoon is great.
After another week, I have to say that I am almost certain I will keep both. The cleans on the 30 are really cool and the edge-of-breakup sounds on the 18 are great. I've had a long day on I'm on my way to bed, but I'll try to post a better description of the two tomorrow
I tried both on Saturday at Cosmos Music in Toronto north. The 30 had a fair bit more power than the 18. I really liked the 30 since it had that Marshall EL34 sound. I found that the tone controls do not have a lot of variation in tone, and what you hear is what you basically get. The sound of the 30 ranges from clean to creamy overdriven. It was difficult to discern at first whether the overdriven sounds were from the power scaling or the preamp section. It took me awhile to figure how the 3 volume controls work since they all work together and none can be seemingly pulled out of the equation. The preamp distortion is excellent and can be easily mistaken from power scaling, for me any way. While the overdriven sound is thick, a recuction on my 68 Strats volume brings me immediately to the land of the clean Marshall. I found it difficult to invoke screeming harmonics, but maybe I just to further crank up the volume on the amp, but I was in a small test room (it would have been real loud). I liked the extra clean headroom of the 30 over the 18. As Pete Thorn has said, the clean sound of the 30 is awefully great sounding. The 18 can't get there, especially with that kind of kick. The 18 has more chime and a smooth creamy sound everywhere, but not that wicked kicking clean of the 30. As you crank up the 18 with all of its controls, the total volume does not climb anywhere like the 30. It doesn't have the cubic inch iron of the 30, but the 18 would be OK if you have a quieter drummer along with other quieter band members. After having played EL34 amps all of these years, the 30 is from familiar territory for me. If you like EL34's, the 30 probably has your sound. The 30 has extra speaker jacks for different impedances and a standby switch (and a loop I think). The 30 felt heavier too, about the weight of an older 50W Marshall head. Both heads sounded very good through the Suhr 12 cabinet. They heads and cabinet look great as a mini stack. You are not going to get a Robben Ford sound here from either of them, although I understand that your can switch the EL34's for 6L6's if you like. I came close to buying the 30 but another amp I saw elsewhere attracted me even more, especially for its versitality, and power scaling, and I may tell you about it in a couple of days, if you want. But the Badger 30 does the EL34 sound great justice and I would be hard to beat it with anything for that Marshally EL34 sound - quite awesome.