Your key criteria for brand purchase is based on 3 factors, these as defined by you are:
Let's take each one of them individually and evaluate.
Maintenance - In case of maintenance one incurs cost of parts, oil and labour for paid service and labour and oil cost for free service. Maintenance also gets affected by standard warranty, which protects many parts of the car while it's valid. Warranty along with car insurance are two big peace of mind providers.
Sail comes with GM/Chevrolet's 3 years/100000 Kms standard warranty as against this Dzire comes with 2 years/40 kms warranty only.
Chevrolet Sail also comes with Chevrolet's unique benefit of 3 yrs/45000 kms (whichever is earlier) Chevrolet Promise. This means that basis prescribed service schedule, your cost towards maintenance is fixed and if in case you pay more than what is defined as per the service schedule, that additional spend will be refunded by Chevrolet (T & C does apply). However, Chevrolet also offers 3 years /45000 kms service package (additional cost), which is great because it covers, labour, parts and even some of the time based wearing part, if i am not wrong it covers even clutch plates. Maruti Dzire does not come with any such offer.
Based on Maintenance Chevrolet Sail should be the car of your choice
Comfort - This is defined basis space inside the car, which can be further broken down to cabin space, headroom, legroom and shoulder room. Comfort can also be defined basis the cars riding comfort means whether the ride is smooth or does all the road undulations is passed on to the cars passengers.
American cars are know for their suspension, which are tuned more for passenger comfort. Their cars ride is pretty controlled and suspension does absorb lots of what the road has to throw at it. Ride quality of Sail gets a rating of 9/10 and Dzire is rated at 8/10.
Sail is longer by 250 mm over Dzire. Wheel base of Sail is more by 35 mm over the Dzire, means more cabin space. Whilst width of two cars is comparable (1690 mm for Sail and 1695 mm for Dzire). Dzire though will offer more headroom of almost 52 mm over Sail.
On comfort we will still recommend the Chevrolet Sail, thanks to its ride quality, longer length that gives you more boot space, more cabin space, equivalent shoulder room but lesser headroom over Dzire.
Safety - Its mostly feature driven and all car manufacturers load their top end model with best of safety features, however, if one buys middle to lower variant of any car model, safety is just a word. Safety also matter when one stretches the car, which in Indian traffic is normally not possible, however, when on highway, safety features do matter. Saftey is also measured basis build strength and safety ranking of a car. Build quality rating of Chevrolet Sail Vs Maruti Suzuki Dzire is 7/10 for both cars. Safety rating too at 8/10 for both cars is same. Therefore on safety parameter, we will rank both equally.
It's quite obvious that, as Sail ranks higher than the Dzire on 2 out of 3 parameters of your choice, we would recommend the Sail over the Dzire.
We at www.ecardlr.com also recommend and exhaustive test drive of all cars in your consideration set. Define your car need in as much details as possible, read various reviews and take our inputs as suggestion only and not a final decision.