For my money, the novels produced during ENT's run were sub-par until Last Full Measure. I'd recommend reading Last Full Measure and then jumping into the relaunch with The Good That Men Do and Kobayashi Maru -- but make sure you don't do that until you've seen ENT's last season.
Funny, I would recommend the exact opposite. Read those published during the run of the series (since even the weaker ones were at least average in the worst case) and ignore M&M's Enterprise stuff since those get worse with every installment.
To each their own I guess but I couldn't disagree more. The M&M stuff was some fantastic reading.