kinda comes down to a number of things.
1: Procurement, if you are ordering a relatively small number (say 20 or 30), the FX1E is faster, more upgradeable, higher tech, and only marginally more expensive. Unless you are on an extremely tight budget, it is probably the better choice. If however, you are ordering them by the thousands or tens of thousands, then that small per unit cost difference makes a difference... Doubt you are on a tight budget if you are ordering 5k to 15k though...
2: Intended operators. If this machine is intended for inexperienced drivers than the FX1E is again, the better choice. The DHS make it impossible to overheat the machine, and for most lights speed is life. As an aside, doesn't the -1MP due to heat also cause the running movement to be recalculated (or am I confusing my rule sets)? If so, then 7/11 -1 is 6/9. Such things can be important.
3: Production. Usually lower tech is easier to produce. Can be handy if your faction has either limited or vulnerable production facilities. Keep in mind that the most vulnerable process is the measure of how easily production (and possibly repair) can be disrupted.
4: Maintenance. How good are your techs, and the training system that produces them? If any guy who graduates from your states' tech school is fully capable of maintaining the FX1E, then that is probably the better option. If not, lower tech is usually easier to maintain...
5: Placed here because I'm sure I missed something.....
Interestingly, as a "What would I do?" exercise. I'd put the TAG on the FX1 in place of 1 ML, LPPC+ML=8 heat, add 2 for running (=10) and no overheat.
The FX1E has WAY more cooling, LPPC+(MLx2)=11 heat, add 2 for running (=13) still no overheat. Should we maybe put ERMLs in there (still only 15+2 heat)
If I could squeeze one more ton outta the 1E that would make me so happy (third ERML or TAG). Maybe a small cockpit? This though, starts to redesign the machine...
Hope that helps...