I would think that your best option is going to be staying west of the Merrimack River. Londonderry would work, but that would mean jumping on 93S with all the other thousands of commuters. Route 3 is more direct to Lowell, and runs directly down from Merrimack/Nashua into Tyngsborough, and on to Lowell.
Amherst is very nice, but you're right, it would make for a lengthy commute. How about Hollis? The schools are very highly rated (check w/ lisa g, a regular on this NH forum) and a nice thing about Hollis is that you have farms and barns etc. in town, and a short drive away is the conveniences of shopping, restaurants, etc.
Where are you relocating from, and how long before you come here to New Hampshire? Keep us all in the loop
Oh and welcome to the NH forum...