If you've got $5k to blow and don't mind having that kind of cash tied up in a HD/Truck gun, at the risk of it being stolen or winding up in an evidence locker, then the real deal HK94 conversion is the answer.
Some folks place a lot of emphasis on "licensed" copies being the second best thing, but it has been my experience that this is a very misunderstood area. In reality, it simply means that they're paying royalties to HK to be allowed to produce the guns, and in some cases, they are using equipment that either belongs to or was purchased directly from HK. Make no mistake, there have been plenty of issues with both MKE and POF guns. Making a firearms with given blueprints on factory equipment is one thing, but things like the technical specs of the steel and the level of QA and QC are things that are not guaranteed, regardless of whether or not the manufacturer is licensed by HK to make an MP5 clone. Examples of this are MKEs with broken locking pieces and POFs with crooked triple trees. These types of things don't happen with the original German guns.
For the clone world, I suggest looking at the project in terms of a barreled action and go from there. RCM (USA) makes extremely high quality bolt groups and barrels. In fact, were it not for German proof marks, you'd be hard-pressed to tell the difference between the two. On the other hand, there are no US-made trigger groups that are worthwhile; they're almost always cheesy plastic housings with out of spec ejectors, hammers, etc. For this reason, I usually recommend using RCM bolt groups and then going with a German semi-auto converted trigger pack and grip frame. This gives you high quality components while also keeping the cost down, since HK bolt groups usually cost more than most people are willing to pay for a complete rifle.
Through planning and some buy-sell-trade action, you can have a reliable MP5 clone for $2k or less. Of course, there are people out there whose clones have not needed any corrections, but you can't always depend on that result right out of the box.
For me personally, I think a $2k +/- MP5 SBR isn't something I would want to use as a truck gun. For my uses/perspective, a cheap, easily replaced AR makes more sense.
If you are willing to pursue the components and buy-sell-trade to get your MP5 set up the way you want it, then I'd recommend looking at the current DJ Getz offerings. If you want it to be ready to rock right away, then pony up the extra cash for a Dakota Tactical. Another somewhat more expensive option would be to get a hold of a German kit and have a custom builder put it all together for you.
Mine is an older Bobcat barreled action with an RCM bolt group and a German semi-auto converted trigger group in a clipped and pinned SEF Navy style grip. The gun is extremely reliable, very accurate, and super quiet with the can and 147s. I certainly trust this gun, but that's because it has proven itself to me over the years. My only regret is not having taken this project on earlier!
