if you also want a total players opinion, imho 1.7.1 is still better in mp, simply because we only had one desync so far in countless games, some of them over multiple sessions, one even - as i fell asleep while others continued - over almost 20 hours without any issues;Long story short: what is the better branch to play MP right now? 1.6.1 or 1.7 ??
hotjoin filetransfer is also really fast, generally the game usually runs better, and so far even mods work
It kinda totally changes the feeling, if you can just hop in into some game, play a while as guest, and since therefore you can also easier play larger maps with initially less people; well if you are a corvette spammer who likes to end games quickly, that might not be so cool.
downsides are no steam join, some people having issues with getting their game found, and if you are behind a router with someone else, and none of you are hosting, one either has to use a vpn, or hope it works.
I am not sure, how both are mechanically different (balance hotfixes in 1.6.x), would be interesting to know. but I guess since Krille's statement says use 1.6.1 for "proper" games, they might differ.
i would not allow people to hotjoin in a running session in 1.6 line, generally it however works fine to continue a savegame with a closed group, if everybody hotjoins right at load.