If you primary focus is getting a skirmish worthy gun then the TM is the clear winner. Externally the Umarex is the right size and does have the nicest externals of all the MP7 variants but the internals are made of cheese (fine if you want a wall hanger that will occasionally fire a few shots in the garden to impress some friends, but not really good for anything else).
When I really wanted an MP7 I just couldn't get over the size thing, the TM was just too toy like for me (some people do consider the reduced size a plus e.g. if they want a secondary to a sniper rifle). I ended up with a WE and am reasonably satisfied with my choice. Its shooting performance is no where near as good as the TM and its not as pretty as the Umarex, but it is functional and robust and does have the best sound and kick of all the variants, it also feels sufficiently heavy and solid that you can suspend disbelief that its a real firearm when skirmishing. The heavy metal bolt does mean it is nowhere near as gas efficient as the TM and it does suffer some cool down if you try and dump a whole mag in short order. It is noticeable if doing repeated bursts at the range on a target, much less so when skirmishing (assuming you are not using it like a high-up equipped AEG).
