There are some fine Chianti and fine Brunello. It is impossible to say that Brunello is better though, because of the 177 or so Brunello produced in a given good year, only about 30 or so are truly substantial wines. The bulkk if Brunello production is ordinry at best and quite a bit of it is poor. This is because the DOC is growing rapidly and most of the plantings are on the newer side and most of the wineries only recently began bottling their own wines. Having said that, in my opinion, the best of Brunello is incomparable. Just as the best of Chianti stands to be judged on its own. In my taste, I prefer a great Brunello to a great Chianti in general.
Chianti is grown in a large area, stretching from North of Firenze to the lower hills around Montalcino, from Arezzo to Lucca. So it is a huge area with many sub divisions and zones of production. The most famous is Chianti Classico which is centered on Greve, Castellina and Castellina in Chianti. The dominant grape in Chianti is Sangiovese with about 10% being allowed to be any other grape the producer wants. Different zones have different specific requirements. Riserva needs more aging in barrel. There are many schools of winemaking in Chianti. 100% Sangiovese, 90% Sangiovese and the rest wither cabernet or merlot, traditional grapes, Botti, Barrique, combination wood regiems etc etc etc.
Brunello must be 100% sangiovese of the Brunello clone grown in the fairly small zone of Brunello di Montalcino which surrounds the town of Montalcino about 5 miles north and south, maybe 3 east and west. Een in this small area, there are over 14 soil types (some argue 22 or more, its basically a numbers game) and at leqast 4 major growing areas. Brunello needs to be aged 3 years before bottling and then spend a further year in the bottle before release. There are three main schools of winemaking in Brunello. The traditionalist use on the large Slavonian oak Botti usually hundreds if not thousands of liters in size for the full three years of aging. There are modernists who use small french oak predominantly. The middle ground is for all of the wine to see some time in small barrel and the rest of the time in botti.
I find Brunello to be more of a layered experience. When well made, it is full of fruit, spice, earth, mineral. With some age, it shows mushrooms and truffles on the nose and a smokiness often develops.
The drawback of Brunello is that it is relatively expensive. Rosso di Montalcino is the younger, less aged wine released from Montalcino. Now the 2003 Rosso are just coming to market and can be found for about $30 a bottle, about what you would pay for a good Chianti Classico from a top producer. 2001 Brunello are about a year away from the US market and will run about $60 a bottle, what you would pay for a good Super Tuscan from a top producer.
My favorite producers year in and year out are:
Pertimali Sasetti Livio
Ciacci Piccolomini d'Aragona
Costanti
Agostina Pieri
Collosorbo
Cerbaiona di Diego Molinari
Salvioni (Cerbaiola)
Le Chiuse
Gianni Brunelli
I have really liked recent vintages of Romitorio and when Siro Pacenti is good its off the map, but some off vintages have dissapointed.