Could go either way. I don't really care much for the first instalments of either series, as Budokai 1 had little going for it beyond the cutscenes and some alternate costumes when compared to its successors whilst Budokai Tenkaichi 1 had overly simplistic combat options to the point that guard breaks + gut punches were overly broken. Still, Tenkaichi had a far more expansive story mode, character roster and interesting modes such as Ultimate Battle, so I'd give the win to Tenkaichi.
The 2nd instalments of both games are both likeable for very different reasons. Budokai 2 is pretty poor in terms of storytelling, but the unique aspect of its story mode and scenarios made it a lot more fun than the constant repeating of the Z story seen before and after it, as well as the cool what-if characters. Tenkaichi 2 had the most expansive story out of any DBZ game and its other modes such as Ultimate Battle Z offered a lot more than Budokai 2's modes did. Overall, I'd give the win there to Tenkaichi 2.
Finally, the third instalments of both games were the pinnacle of DBZ games. Budokai 3 had the more fluid combat mode and more interesting story with how its exploration could result in what-if scenarios, not to mention having the best ost out of any DBZ game. Meanwhile, Tenkaichi 3 had the biggest character roster, more options when it came to tournaments and alongside adding the features to Ultimate Battle from both its predecessors, added in the innovative and challenging mode of SIM Dragon. Overall, I'd say Tenkaichi 3 had more going for it as a long haul to keep you playing whilst Budokai 3 made the better option as quick fun. In the end, I'd say Tenkaichi 3 wins as comparing it to its predecessor, the only thing it really lost to make it not be the ultimate culmination of all that had came before was the story mode. Compared to that, Budokai 3 missed out on a lot more by not including the what-if characters from the previous game or some of the stages such as Muscle Tower, the former of which is disappointing when considering the effort put into making many alternate scenarios in story mode.
So, with things tallied up, I'd overall give the win to the Tenkaichi series.