I Hate To Do Rankings.

But Chris called for it;) 

In terms of submarine technology, how would you rank countries?
1. Russia with the U.S. being a close second (or maybe first). I doubt that there is a close second
2. China
3. Germany
4. France
4. Iran

Submarines must be difficult to build because very few countries do it. I didn't bother to rank the U.K.

OK. Here it is. Agree--subs are the most complex systems humanity builds, even more complex than ISS. So, here are my rankings:

Nuclear-powered subs. 

SSBNs (Strategic Missile Submarines). 

1.Russia

2.US

3. France

4.UK (doesn't have own SLBMs)

5. China.

SSNs (fast attack nukes).

1. US

2. Russia

3. UK

4. France

5. China

SSGNs (cruise missile nukes).

1. Russia

2. US

3. The rest of the world. 

SSKs, Non-nuclear subs.

w/o AIP. 

1. Russia

2. Japan

3. China

4. Germany

5. The rest of the world.

SSKs with AIP.

1. Sweden

2. Germany

3. Japan

4. Reportedly China

5. The rest of the world. 

Also, keep in mind--submarine, no matter how good, it is still a platform. These are the weapons which it carries which make it into a complete weapon system. In terms of weapons on subs Russia simply crushes competition.