One of the best features about Match.com is their search - if you do a search and don't like certain members, it gives you the option to remove them from the search results and will never show them again! This is great for streamlining your search for a date - Yahoo doesn't offer this.
Match.com definitely seems to be more a 'hip' site and has a great look and feel of the site! Yahoo can be simple in some places, but sometimes this is good because it makes using the site very easy.
Yahoo Personals is actually cheaper than Match.com - its basic price is $19.95 a month - Match.com is $29.95, but they offer a free 3 day trial! Match also has a good deal though - you can lower their rate to $12.95 per month if you pay 6 months in advance!
Yahoo Personals offers free icebreaker lines to show your interest without subscribing - Match.com only offers a winking system to let someone you know you are interested in them for free.
Yahoo Personals suffers from its rather simple profiles too - it doesn't have as many interesting sections or questions like Match.com offers, even though it has a better instant messenger - it uses Yahoo messenger!