I have played most of the rulesets already mentioned...
WMA is a very good game, fairly simple, but with the bucket load of dice approach. The best thing about it is the command and control mechanics. It can be very frustrating when your planned flank attack stalls and your troops stand about doing nothing, but, such is war
Id put a link on for a battle report, but Justin beat me to it! That was a good game
Impetus grabbed my attention a few years back, and i built a few armies for it, but there is something that doesn't sit right with me about it, some of the army lists are a bit odd, and the abbreviations, being in Italian doesn't make it easy to remember. The cohesion test can and does ruin the game. As Justin rightly said, its too luck dependant. The best thing about it IMHO, is the basing.
Impetus battle report - http://yorkie.6sided.net/2010/12/10/the ... of-towton/
Hail Caesar for me is the best Ancients game out there at the moment. It seems to be a development and improvement on WMA, its very easy to pick up and with a flexible basing system it suits me very well. I use my Impetus based units and it works fine, i have played it with WMA based armies and its ok too.
Heres some of my thoughts on sorting out 15mm figs - http://yorkie.6sided.net/2011/07/07/hail-caesar-greeks/
If i was starting out in ancients, i would definately go for Hail Caesar, with 15mm figures. Just my 2p