I recommend General de Brigade. I have not tried Republic to Empire but I have tried BP, Shako2 and others. GdeB is a good balance between realistic rules that accurately reflect Napoleonic tactics and quick play rules. It is scaled for 25/28mm and 15mm figure scales…inches for 25/28mm and cms for 15mm…throughout the rules for quick reference.
I like the look of the 20:1 ratio units on the table top…they look realistic. The size of units forces one to consider the appropriate formation for the unit vis a vis the terrain, particularly a battalion in line. I also like the orders regime that forces one to think ahead knowing that orders are not executed when you wish them to be. Further, the orders mechanism mitigates the 'sky general' aspect of most games. Units within a brigade must operate within the order constraints.
Most importantly, I like the morale system that applies to units, brigades and divisions coupled with Army Falter and Break Points. This provides more realistic play so that units do not fight until the last man standing. Most scenarios are geared for divisional size battles, however, there are optional corps rules if needed.
An important issue for me is that there are no rosters or sheets to keep track of. As long as your units are labelled, and you have a method for dealing with casualties, you need only the QR chart and the rules, if rule detail is required. Markers for orders and actions can be downloaded from the blog site.
Also, Gde B has an active forum to discuss the rules and their possible interpretations. The GdeB blog is overseen by the rules author David Brown. I find this blog most helpful.
A great set of rules and highly recommended.