What criteria (objective or subjective) is good to use when evaluating a currency (crypto or fiat) and its associated payment systems. You could look at a cryptocurrency by itself, how it compares to other cryptocurrencies and how it compares to fiat currencies. I think we also have to be careful to look payment methods as separate issues, though they are affected by the currency they make payments with.
Criteria for currencies
1) Store of value - how well does a currency hold its value over time,
2) Unit of account - is the currency highly divisible with great precision, is the currency fungible
3) medium of exchange - is the currency widely accepted as payment for goods and services
BTC is a good store of value and a good unit of account. As a medium of exchange it has a long way to go but many improvement have been made in the last 12 months.
When looking at payment system for transferring BTC from one party to another
1) how many people use the payment system (e.g. the bitcoin client)
2) to total value of all the payments going through the system in a period of time (hour, day, month, year).
3) is the payment system being improved or developed
BTC the currency and the payment system have some good thing going for them. Leave your observations about BTC vs other currencies and payment systems.
I have a lot of experience with the USD so I'll comment on it. USD is a widely accepted medium of exchange and a good unit of account. As far as a store of value, the USD has been slowly losing its value over the past 100 years. I believe its lost about 95% of its value since 1913. Although this loss is gradual the cumulative effect is large over longer periods of time.
The are many USD payments systems: cash, check, ACH, bank wire, paypal, dwolla and credit cards to name a few. Many of these methods are subject to chargeback risks which you need to be aware of if you accept that payment system.
Share your thoughts here as if it were an open thinktank.