Your friends can buy bitcoins and other cryptos in:
1. Coinbase
2. Bitstamp
3. BTC-e
4. MtGox
5. Bitfinex
6. BitcoinAverage.com
MtGox wasnt good idea as of now ,since they have lots of legal issues to tackle
Most of what you suggest is better option but for me local exchange is best for then,if only they are in my location theres no hard to buy bitcoin because in local wallet you can purchase bitcoin and ethereum