I'm assuming that whoever is paying you for decay is wanting the most eco set up so they don't waste money. That being said, I think people are going to choose a FAP90 over a ek-2600.
a FAP 90 is abit more eco according to entropedia 2 pec less cost per use. for only 2 health less.
Even if you have a tier 2 EMT-2600 with eco enhancers the FAP-90 without enhancers would still be more eco.
If you starting a fapping service you need to take into account that the customer will be more willing to use your services if you can provide cheap heals and keep him alive offcourse .
I have a emt-2600 myself and i must say its really not eco if need to use it alot.
if you wanna skill paramedic i would look at your skill and what L tools you can use. ( if you want to use L at all That is )
With a maxed T15 you can do some healing service of course (little levis,some robots..etc..)
-->if you need a quicker fap you can also look at the adapted T15...(nice for event creatures like Longtooth)
-->the it comes to T20 and Hedoc Sk-50 ... but this takes some time...