As Matches points out, the best one is the one you have with you. Personally, I've chosen the Leatherma Wave (original) on my belt and a Victorinox Manager in my watch pocket backed up with a Cybertool 29 and Wave Tool Adapter+extra bits in my bag. I find that I have practically all situations covered with this combination. If you're going to keep it in your backpack, then bulk probably doesn't matter that much so your options are very open. Here are my suggestions, all are from companies who have a reputation for quality. I haven't owned the recent batch of LM (new Wave, Charge, Blast or Fuse) or the Spirit, but I've owned/used all of the others at one point or the other.
Heavy duty: SOG Powerlock, LM SuperTool 200 or Blast, Swisstool-X. All four are top notch quality (with the nod going to the Swisstool for final fit and polish). These are all heavy duty tools, capable of very hard use. Of course, you pay for this strength with added weight and bulk. Since you're looking for
Medium duty: Leatherman Wave, Charge, or Fuse; or Swisstool Spirit, Cybertool series. All of these will cover most of the needs you will encounter. With the new beefed up pivot and locking mechanism, the Wave and the Charge might even be considered heavy duty but fall slightly short of the sheer robustness of the onces in the heavy duty selection. The Cybertool 34/41's pliers fall short of medium duty, but the included bits with its emphasis on technical work make it a better fit for "urban" work.
Since you're looking for the "ideal urban tool", I don't think you should bother with any in the Juice line, as I consider their pliers and tools too light for any but the lightest of tasks..
Among the ones you mentioned, I'd suggest the Swisstool with the optional bits and tools. The Blast hits a sweet spot for price/performance, but isn't what I'd call ideal. If you are partial to Leathermans, the Charge/Wave are excellent options but lack an awl. If you are going to be doing alot of electronic/technical work, the Cybertools are very good compact choices.
Of course, you could follow the Bladeforums motto and "buy them all".

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