Hi noa.
The Starfins is built to order by hand.
The Tropol has moulded footpockets.
They are two really different fins and mine are each tuned for different uses.
The Tropol is much heavier and is negative in the water. This makes it really stable but more tiring to swim with. The blade on my Tropol is stiffer (you can specify stiffness). I would say the Tropol is better for me in the pool. I can do 25m in two kicks with it and it is not affected during glide by currents from other swimmers and does not want to float.
My Starfins has a soft blade - for open water and distance swimming. It is very nice for surface swimming and the blade is very responsive. It is extremely light weight and slightly positive down to about 5 meters. The blade is very springy and gives surprising thrust for how soft it feels.
Both fins perform very well for the respective purposes.
Its important to understand there is a compromise between comfort and performance. A comfortable footpocket is going to be looser on your foot - so there is a sacrifice in force transmission. Likewise - for comfort and recreational diving you will probably want a softer blade (also better for learning). Both my fins are very comfortable - the Tropol probably a little more so than the Starfins but I can wear either one for hours. (with a competitive fit you can generally only wear a fin for 20 minutes or so - and it HURTS!)
With the Starfins the footpockets will be made to order for your feet and Alex has a very good reputation for getting it right (check out the Starfins thread) - the whole fin will be tuned to your body and diving style.
With the Tropol you must pick a pre-made size - they are a heavier fin and also have excellent blade quality and you can select from 5 levels of blade stiffness. (check out the Tropol thread)
I think both are excellent.
My Tropol and I in Dean's Blue Hole and my daughter with her black Starfins.