Cessna 680
The Citation model 680 can be regarded as a blown up Citation Excel. However, it is bigger (longer), has slightly swept wings, double wheels on all landing gears, but no ventral fins. Also the tail is significantly different: with its broader chord it looks a like that of a Lockheed Jetstar. At the front is a small dorsal fin with a curved front.
Citation Sovereign
This is the original version of the model 680. Compared to the later Citation Sovereign+ it has no bent-up wingtips but may be equipped with winglets.
The nose of the Citation Sovereign is more pointed than that of the Citation III and Citation Excel.
Citation Sovereign+
Apart from improved engines and avionics the most apparent external novelty on the Citation Sovereign+, compared to the original Sovereign, are the bent-up wingtips.
The Cessna 680 Citation Sovereign+ has bent-up wing tips as main distinctive feature.
Confusion possible with
Cessna 560XL Citation Excel
The Citation Sovereign uses the front fuselage of the Citation Excel, so they are of course similar. For the rest the Excel is smaller, has straight wings, all single wheel gears, a taller, narrower vertical tail and ventral fins.
Cessna 680A Citation Latitude
Like to Citation Sovereign being derived from the Citation Excel, the Sovereign evolved into the Citation Latitude. The model number of the Latitude (680A) already shows the family relationship. The main differences are the four cockpit windows, length and ventral fins on the Latitude. Also, the dorsal fin has a small air intake. Note that the Sovereign+ has bent-up wingtips like the Latitude, so don't be fooled by them.
Lockheed Jetstar
The four engines attached in pairs to the rear fuselage, large tanks under the wings and a cruciform tail are unique for the Jetstar, but the Citation Sovereign comes close in appearance, especially for the twin engine L-329. However, the Citation has different cockpit windows and no tanks attached to the wings.