The IV is a Corona Gorda which is one of my favorite vitolas 5 5/8 x 46
The III is a Corona Grande which is another vitola I am fond of 6 1/8 x 42
The I is a Perla size which IMO is ridiculously small, it's only 4 x 40. Too bad the Sig I is not a Minuto (4 3/8 x 42).
The II is a Mareva which is another vitola I prefer 5 x 42
The V is a Dalias which is not one of my prefered vitolas 6 3/4 x 43.
If you insist on Cohibas, I'd go with the IV BUT personally, I like the following cigars listed for each vitola over Cohibas in the order listed for each vitola:
Corona Gorda
SLR Serie A
Punch Punch
H. Upmann Magnum 46
Corona Grande
Qd'O Gran Corona
Mareva
WOW, there are so many great Marevas, where do I begin?
SLR PC (If you can find them)
Punch PC del Punch :thumbs: (this is just about my favorite cigar, well this week anyway

)
Ramon Allones PC
H. Upmann PC (this way you can emulate JFK

)
RG PC
Sancho Panza Non Plus
Now, I don't like these but you might, they are all very popular:
Monte #4
Boli PC
HdM Short Hoyo Coronas
I believe that the Mareva is the vitola that is currently available in the largest variety of brands and in the case of some brands (like Punch, H. Uppman and RyJ) offer three different Marevas.