"What is the best bidding system available?"This depends on your goal, the level of opponents, the form of scoring, and many other factors. In my opinion, the best system available is some form of relay precision, if played properly. What I mean by this, is that if you don't have extensive practice and discussion not only on handling interference, but followups to your side's constructive auctions, and detailed agreements in a very large number of situations, you will lose more IMPs from misunderstandings and guesswork, than you will gain from your system advantages.
Therefore, in most partnerships, I prefer a fairly standard 2/1 with a lot of gadgets and modifications. One thing that I would highly recommend is a Short Club with Transfer Responses. Although there are many systems out there, designed to do so many things, sometimes it's best to go back to the basics. Over the years, systems have developed to meet the changing styles of bidding, and to reflect the player's personal styles and preferences. In modern bridge, there is a lot more competitive bidding than there used to be. This makes many systems that used to be superior, ineffective.
A very good example of this would be Canapé-style systems. Before the auctions were so lively, Canapé players could open their shorter suits without any problem: They would have room in later bidding to sort out their hands. Nowadays, when the opponents are in the auction so much, showing the crucial second suit before the auction is too high, is often extremely hard, if not impossible. The style of opening a shorter suit first works in Constructive auctions where the opponents don't bid, however, the more intervention in an auction, the harder it is to actually resolve the opener's hand.
This is also true for a Strong Club system, which is why it does not fare so well with intervention. Even the top players in the world have trouble sometimes with auctions like 1C - (2S) - ?? - (3S). Without these problems, in a constructive auction, a strong club is clearly best. However, with these problems, I feel that a 2/1 style can handle most hands fairly well, and is not nearly as vulnerable to pre-emption.
2/1 has my vote for the best system. Simple is sometimes good.
"If you lived in a perfect world, where you had unlimited memory and practice, what do you think is the best system or combination of systems?"
The above logic brings me to my dream system, which I believe would combine the advantages of both a Strong Club system, and a 2/1 style system. I believe the best system is a combination of the two:
Strong Club when the opponents are Vulnerable, and 2/1 when the opponents are Not Vulnerable.
The value and frequency of pre-emption over a strong club when the opponents are Vulnerable is a lot less. Also, it is much easier to penalize them at this vulnerability. Therefore, when they are more likely to interfere (when NV), the solution is to play 2/1. My personal choice of 2/1 would be with a Short Club and Transfer responses, along with plenty of other gadgets and modifications.
"What would be the best bidding system to learn if I want to learn something new?"I get asked this question quite often. There seem to be "stepping-stones" for learning new systems, sometimes people skip them, but in order to have a full understanding of each system, I would recommend you focus on something that you can understand well.
If you currently only know Standard, or are not very comfortable with 2/1, I would highly suggest you learn and become very familiar with 2/1 before moving to other systems. These two systems are the base of most complicated ones, and understanding them before learning others is vital. If you are looking for some books on it, I would reccomend Eric Rodwell and Audrey Grant's book on 2/1. There is also Paul Thurston's book, and Max Hardy's book. Hardy's book is excellent for advanced players looking for more reading material on 2/1.
If you currently are comfortable with both Standard and 2/1, Precision is the next step for you. Learning Precision will increase your understanding of the system, and make it much easier to play against those who already play precision. I highly recommend David Berkowitz's Precision Today for a fairly simple version of Precision. It is extremely well-written, and covers all the important aspects of a Strong Club system. From there, you can explore other options, for the more adventurous there are Relay Systems available, Daniel Neill has put together an incredible collection of systems at his webpage. Most any system you could possibly want is available there.
If you are comfortable with Standard, 2/1 and Precision and are looking for something to learn for fun, or as a challenge, I'd recommend looking at Daniel Neill's page as well. There is some fun stuff on there that may interest you. Jassem has a very good book on Polish Club as well.
So basically I think there are stepping-stones, as you progress more and more, you'll learn more and more systems. If you're really bored, you can even create your own! Um, not that I've ever done such a thing... :)