Damn...that's a tough one...now that I think about...I don't recall a single solo that I didn't like...well here's my five...I wish it was more like ten...but these are the five that come to mind...in no real order of course...
-Brighton Rock (Live and Studio):Gotta love that echoplex...is really a showcase of Brian getting a lot of kick ass sounds out of his guitar...
-I Want it All: Here Brian flies with his orchestrated precision through the pentatonic forms...
-The Night Comes Down: This guitar part just stirs something in you when hearing it...All of his work does really...
-Too Much Love Will Kill You (Guitar Instrumental
Version): This is one of the very few guitar parts that is as beautiful and penetrating as Freddie's vocal...
-Bohemian Rhapsody:I don't think I need to explain the reason for picking this...legendary.
These are the first that come to mind...I could list off another 10 or 20 that are phenominal...
I love the solos where Brian takes the song to a new level. There are times when he upgrades a song from merely good to great on the basis of his solo alone. Songs I would put into that category are: Back Chat, You Don't Fool Me and of course, Bijou.
These Are The Days Of Our Lives has a rather beautiful solo, particularly the last little bit which Roger ruined in the tribute concert by doing a roll over it.