You should use a similar process to selecting a Fiero that you would for choosing any vehicle among the many available alternatives.
Here are a few considerations:
What style do you prefer? The original more distinctive notch-back or the more common faux-fastback style?
Do you prefer the cleaner sided models without the superfluous lower door and body trim pieces or do you like the additional details?
Do you prefer standard or automatic transmission for the driving you will be doing?
The 2.5L is adequate for normal traffic flow particularly if mated to a 4 or 5 speed manual transmission.
The 5 speed transmission yields better mileage and lower noise for highway cruising due to lower engine rpm.
The 2.8L is more than adequate for normal traffic flow regardless of the transmission.
(If you're on an 80 MPH interstate, the 2.5L won't have much oomph left.)
Do you want A/C or a sunroof for better airflow?
What color do you like? Both red and gold fade significantly with continuous exposure; white is more resilient.
I've had the white '84 SE 2.5L 4 speed since new (May '84) and it's still a daily driver at over 236,000 miles.
I've had the white '88 Formula 2.8L 5 speed since Feb 2008. Purchased with 3,230 miles in showroom condition, now has 23,600 miles on it.
I've had the red '86 2.5L 5 speed coupe since Feb 2011. I swapped in an '87 2.5L in 2013. The car has 85,000 miles on it and shares daily driver duties with the '84.
Except for some maintenance replacement stuff, all are pretty much factory stock. They are garaged when not in use and not used in wet salty weather.