AC contractors - recommendation requested

Two contractors have recommended American Standard, 4 ton central air/furnace. One suggested as a 16 SEER minimum, the model 4A7A6049 compressor and the other suggested the 4A7A6048. Only difference I could determine is the first one weighs about 20 pounds more, holds 2 pound more refrigerant and uses a 1/3 HP fan as opposed to a 1/5 HP fan. It's about $300 more than the lighter one. However, the contractor offering the lighter unit is including a variable speed furnace whereas the other is offering standard high efficiency furnace.

The first one is $7420 remove/replace with a one year service, plus service for my two other AC/Furnace systems. The second one is $7107.

Are these reasonable prices and are the differences worth considering? Also, should I step up to a 17 or 18 SEER and also consider contacting a contractor who uses a different/better brand?