Both systems have quite easy and straightforward signup systems. Both have been around for a while so most names are taken so you may have to add an initial or number. Yahoo and Hotmail both have free email accounts. Both have extra features with their Plus versions which each cost just under $20 per annum.
Yahoo has unlimited storage on free accounts. Hotmail has 5GB. You can download emails to your computer using POP access on Hotmail free. With Yahoo you need the paid for Plus account. Hotmail free accounts expire after 120 days of no activity. Yahoo expires after 4 months of no activity. The Plus accounts of both systems have no expiration limits. No ads in Hotmail free except in outgoing email. Yahoo free has ads on the interface. This can be closed on the New Mail interface. No ads on either system for their Plus accounts.
Both email accounts have a good scanning system for viruses in email and attachments.