Which are the best districts in Vienna?

First time visitors in Vienna will inevitably ask themselves in which district they should stay.

So here is what we suggest.

First of all one must understand the structure of Vienna:

The 1st district is the historic center, surrounded by the famous Ring street. Most sites are here.
Around the first district, one finds districts 2 to 9 which are also pretty central and are also partly historic. These districts are surrounded by the Gürtel: a very busy, large and ugly street, you want to keep away from this one.
And finally, districts 10 to 23 which are out of the Gürtel and partly extend far from the center, all the way to the woods or countryside.

Most visitors will want to stay in the first district. It is indeed the best way to discover Vienna without spending time in the transports. Distances are small and if you stay in the first district you'll easily be able to go back to your apartment/room for a break between museums. Most sites are a very easy walk in the 1st district. The first district also has thousands of shops, restaurants, cafes, you name it, you got it. Luxury brand stores are to be found only in the first district. Public transport from here is amazing. So staying in the first district is mostly positive but there are certain downsides too: it is very touristic, shops and restaurants are usually more expensive than in surrounding districts. This would be my first choice if I had the budget that goes with it.

The second district is partly very close to the center, and you will find a lot of cheap apartments and hotels in this district. And they are cheap for a reason. Except for the area surrounding the Augarten, a very nice, large park,  which is an enjoyable, laid-back neighbourhood, pretty much all the rest of the second district is clearly second choice, often ugly buildings from the 50s, not the safest part of Vienna either (but still safe enough, Vienna is a safe city in general). So except for the Augarten area, where public transport is not great unfortunately, this district would only be my last choice (but still a choice, some other districts I consider as no choice...).

The third district is only recommendable in its part closest to the Ring street. It is a district with no clear personality. Still, not a bad choice if you get a good deal very close to the Ring (200 meters max).

The 4th, 5th and 6th are nice districts: choose to stay near transports, and in the half that is closer to the Ring.

The 7th district is the bourgeois-bohème district of Vienna, very enjoyable, with loads of restaurants and cafes that offer good value, as well as Vienna's biggest shopping street, the Mariahilferstrasse.

The 8th district, is not very well served by public transport and it's a shame because it is very nice, with a very "small town neighbourhood" kind of feeling, that makes one just want to stay and live there forever...

The 9th district is large, and the area closest to the Ring is one of the nicest upper-market in Vienna. It has an amazing public transport network, and is very safe due to the presence of several Police headquarters.

A nice apartment/room near the Ring in districts 6 to 9 would be my second choice.

Districts 3 to 5 being my third choice.

Concerning the districts 10 to 23, well these are quite far from the sites and the center. Some of them are very nice indeed (13th, 19th), others are a mix of industrial zones and sponsored housing (10th, 11th). I wouldn't recommend the average visitor to stay in any of these districts.

That's it and it is only my opinion.

What do you think about Vienna's districts (in the perspective of a visitor)?