Three years back in 2014 I purchased 2 bikes for myself. A Trek FX 7.3 and a Specialized Sirrus Sport. in those 3 years of ownership the bikes had some key flaws, this is meant to be a sort of buyers guide from someone who has owned both.
Trek FX 7.3
As a fitness bike the FX definitely did its job, as a fast, reliable and comfortable Hybrid style bike. 
Some pros for this bike are :
Price : Sitting pretty at $660 USD the FX has a great value as well as an incredible lifespan on the parts.
Lifespan : Upwards of 5 years, through all the abuse this bike has been through the parts on it have never given out underneath me and the internally routed cables greatly help in reducing trips to the local bike shop
Components : This is make or break for Hybrids most of the time. The Shimano Tourney Derailleurs both front and rear have no problem shifting through the entirety of the 27 different gear combinations. the brake arms are sturdy and rugged, the wheels arent anything to write home about but they wont let you down either, and lastly, the handle bars. On a fitness hybrid, the main draw to it is the upright fitness position, the bars support around 20% of your weight and having the Isozone Handlebars and grips really makes it feel like less than even that.
Cons : The seat is unlikely to win any comfort contests very soon so i do recommend buying a different seat outright. I literally cannot think of any other cons.
Bottom line : Since this is an older model I cant go out and tell you to buy this one, as it wouldn't be very easy to find in all honesty, most people are quite attached to theirs as I am mine. The newer Trek FX' models are something to behold though, now offering Hydraulic disk brakes on all models of the FX above the FX 1. All things considered you would be hard pressed to find a better bike than an FX in terms of quality and comfort overall.
Specialized Sirrus Sport
There was not much to like about this bike as a whole, some small upgrades in components don't save this bike from being anything more than a beater sadly.
though few, there are some pros about this bike when compared to the Trek FX 7.3
Pros : coming equipped with Shimano Acera shifters and derailleurs is a pro however minute it may be. The already harmonious shifting of the Shimano Tourney isn't far behind, but the Acera is better nonetheless.
Price : $600 USD : though the price is lower, the quality suffers significantly (see below)
Cons : same type of seat as the FX 7.3, quite uncomfortable and hard, though the similarity in lack of quality ends there. The Sirrus Sport lacks many things but comfort is the most glaring aspect, the bars and grips were quite hard and uncomfortable. Many times I noticed numbness throughout my hands and aches in my elbows after a ride. the overall responsiveness of the frame was also lacking, it felt as though it was flexing and bending harshly during sprints which caused a lot of power loss on the down stroke.
Lifespan : sadly I cant say much about this besides the fact that I had to take the bike to the shop at least 3 times a year to replace frozen cables. The frame and wheels are doing okay but most of the bolts on the bike are also beginning to rust and I cant say i'm too pleased with the quality.
Bottom Line : dont buy this bike unless you have a lot of disposable income to take it to the shop for repairs and sink another $200+ into upgrading all aspects of this bike. unresponsive, slow, uncomfortable and poor quality on 90% of the parts.
All things considered , the Trek FX series has been going for a long time now and it really shows, their attention to detail and build quality is unmatched in almost all areas. Buy a Trek FX and you will not be disappointed.