I went the 'laptop + lg 5k' route as my primary and came to regret it, fast. Stability was lacking at a time that if I lost my computer, if even for a day here or there, I stood to lose everything (extraordinary circumstances).
I remedied that by acquiring a spankin' new iMac for pc of mind. It's the best pc of kit, save the mac pro's that I haven't experience with so can't comment, that Apple offers when it comes to stability and reliability.
Coming from mbp's for daily use, it was (and still is) refreshing to work on a desktop again, bc there simply is no comparison in my view. But, that means you're chained to a desk, though..ugh!!
Never mind the naysayer's that suggest a new 21" iMac is somehow a 'subpar' iMac..b/c that's just silly. I wouldn't trade mine for anything, plus, it doesn't look horribly disproportionate setting atop a standard desk. Comment's not intended to dog the 27" by saying that b/c in some aspects, it is indeed a bit of a better value, but certainly not in all..that paints with too broad a stroke to suggest such a thing imo. For some, the 21" is the right tool for the job and at the end of the day, that's what matters.
Coming from a laptop, of any size, the 21" is roomy..at other times however, the extra screen space is nice on the 27" (eg: multiple docs)
Hard to go wrong with an iMac.