My top 5:
1.) France/England
2.) Turkey/Italy
3.) Italy/Austria
4.) Russia/Austria
5.) Russia/Italy
Runner up: France/Germany
I/T is amazing, but it takes an enormous amount of trust on both ends (because so much territory is left available in the Austrian mainland - I don't try this often). E/F is very good but I find that England tends to stab France, some earlier than others. I like this one to run it all the way to the end in a 17/17. I/A is very good, we all understand the lepanto. R/A and R/I are both equally effective, but I put R/A higher on the list because it's better for Russia to have an immediate ally, even with Turkey, assuming that northern pressure is coming.
I also like the Mediterranean Triple. I/A/T.. Italy take the western seas, Austria the midland, and Turkey carve up Russia, waiting for Italy's assistance to complete the game in Scandinavia. It's very secure and hard to stab, but many people don't like the early resolution of a three-way draw, which often scares people off quickly.