My interest in DIY audio started with speaker cabs. I have come to favour transmission lines and dislike bass reflex immensely.
My fullrange studio monitors (the prototype natural pair for my house/my wife, white pair for my studio and red pair for my little bro):


These are designed to be wall or soffit mounted making them ideal for use in smaller rooms. That's only a 4" driver but due to the TL loading and wall placement there is no shortage of bass. Amazing stereo imaging due to complete lack of crossover and point source of sound.
I also built what started as a 2x12 lead/bass cab (a bit smaller face than a 4x12, but deeper) but was sawn into 2 1x12s when I realised it wouldn't fit into my then bass player's Civic. It's much more usefull that way - keep one at the studio and one at home:


They have the midrange clarity and detail of an open back with the bass response of a sealed or even horn (yet still not too boomy when used with a bucker equipped guitar). I like the one with the Marsland (Jensenish) for guitar and a JBL or EV for bass. It'll take any guitar speaker with an Fs of 65-85 (which is 99% of guitar speakers) and have enough low end extension for bass use (gotta love those TLs). Maybe even a wider range if you're willing to play with the stuffing.
And in a moment of poor judgement I built this monstrosity (loaded with 8x10" vintage pre-celestion Rola alnico magnet woofers):


That's one of the Lead/Bass cabs with the grille on on the left in the last pic... and the middle cab is not a Traynor (came to me that way, which is why I got it as cheap as I did) but actually a Musicman 115RH - a very nice cab indeed (reflex horn). They greatly benefit from replacing the stock Eminence stamped frame driver with an EV cast frame one (there was an option for a factory upgrade; pity the fool who didn't take it).