This is a one-way recommendation. Those who enjoyed Spice & Wolf are likely to enjoy the Banner of the Stars series, but not necessarily vice versa.
The relationship between the two main characters is an integral part of both series, although it is not always what drives the plot in either case. Similarly, a great deal of attention is given to dialogue in both cases: In Spice & Wolf this almost exclusively comes in the form of competitive banter and wittiness. However, in Banner of the Stars the banter between the main duo tends to be less competitive and there are more genuine discussions. />
On these merits alone one might be able to recommend in either direction, but the primary distinction between the two anime is their usage of their setting. Although the setting of Spice & Wolf is well designed and occasionally plays into the events of the plot, the setting of Banner of the Stars is far more relevant both to the relationship between the two leads and to the events of the story. That is, in Spice & Wolf any conflict can almost always be pinned on one of the leads, whereas in Banner of the Stars larger cultural conflicts have both direct and indirect effects on the leads. Because of this, the way the leads' interactions relate to the greater narrative context won't feel the same (which is to say there is very little greater narrative context in Spice & Wolf). At that, many may find the cultural conflicts of Banner of the Stars to be easier to digest than the economics of Spice & Wolf. It is for these reasons that I mostly consider this a one-way recommend, with the inverse being recommended only cautiously.
Action is more prevalent in Banner of the Stars than in Spice & Wolf, but like Spice & Wolf, you will likely be bored if you're only coming for the action.
Finally, although neither anime series covers all of the source novels, the ending of the Banner of the Stars series is far more conclusive and satisfying than the ending of the Spice & Wolf series. In fact, it is very likely that those unaware of the Banner of the Stars novels wouldn't realize the novels were still ongoing in the first place.
In the end they are both excellent series with similar positive traits, but I consider Banner of the Stars to have broader appeal and better cohesion between the characterization, setting, and themes. If you liked the former, be sure to check out the latter.