When you say "monitor", do you mean smaller 2-way speakers as monitor speakers instead of full-height floor standing? Or do you mean speakers from the "Monitor Audio" brand? You're saying that the monitors can be up to 50" tall (which is a very tall floor stander to me), so it is confusing what your question is.
I think it may depend a lot on the type of electronics/amplification you have. I am biased here, but the B&W 805 bookshelf speakers have incredible amounts of bass/punch/body for the size. -- given that you have a good high current amplifier driving them. They have been around for several generations of versions (I have Diamond gen 2). I don’t know how asthetic you need, but they can be found with rosenut or cherry finish. The piano black is very nice, but the flat black is not so much.
This question of "what speaker" is likely to spawn a million opinions :). To be honest, there may be several choices that are nice.
Assuming you will use a subwoofer/subwoofers with this setup and no budget mentioned, Klipsch Heresy(Heresy II, Heresy III) L-C-R makes a great HT front stage. Dynamics, tight bass, low distortion. Your price of entry for triple Heresy I's or HII's could be as low as $700.00 or if new triple HIII's around $3000.00.
Well, if you would DIY it I would strongly recommend my kits the LM-1 and LM-1Cs. Designs are free. Parts are in line with $1,500 to $2,000/pair speakers (depending on which and choice of caps).
Also, very dynamic and neutral. They are small though, so don't expect a Swing Orchestra level performance at full volume without a sub. however the midrange is very lively, treble is neutral and extends to 30kHz.
Plus, you get to tweak absolute tweeter settings and cap values. :)