YaY! Another Sonic/Sonic!
I've just rolled myself one recently, still exploring it more indepth.
Howls good for me, I like it on top of shout. 
Eheh. Sonic sets are quite nice (except the graphics and sounds). I'm L22 now and I picked Disruption Field. Tbh I don't like it much. I might respec it off and pick Assault and Tactics.
@False Fiction - Virtue / Defiant
Current projects - [Glaciologist - Ill/Cold Troller] [Cloudshaper - Storm/Dark Def] [Harald Wartooth - Elec/Psi Domi]
Well i have got my Sonics/Sonics up to lvl 36 now and its been an interesting career but regards to your question, well;
Disruption field, I personally took and quickly regretted it, its a big endurance user and because Brutes unlike Tanks cant manage aggro that effectively the said aggro would turn on me, unless i was hidden behind a wall or something. So for me it was a big no no.
Howl, again i took this power and respecced it out again, i found that i was only teaming in small teams or soloing so howl seemed of little benefit as when soloing i would use Sirens song, Howl would just wake them all up again. But its an excellent power if u team a lot in big teams.
Liquefy, Hmmmm this should be my next power to take, i haven't had any experience with, but i am going to take. All the reports i can find on it say its the worst final power on any set with too long a recharge, not lasting long enough when cast and its effects like KB and debuffs hardly noticeable, but like i said i will take it as i wanna see for myself how bad this power really is.
Ahoy! Straight to the point..
1- Disruption Field and Liquefy. Are these powers any good? According to Liquefy's description I would certainly skip it
2- Howl - Should I pick it? I mean.. Shout does greater damage and the recharge time is the same (according to my builder).
Cheers
@False Fiction - Virtue / Defiant
Current projects - [Glaciologist - Ill/Cold Troller] [Cloudshaper - Storm/Dark Def] [Harald Wartooth - Elec/Psi Domi]