Hal, who is otherwise known as Prince Henry of Wales and the future King of England, is very different from his counterpart, Hotspur. Hal enjoys a good time, and expends his energies plotting pranks with an unsavory element at the pubs. Although he is being groomed to one day be King, Hal avoids his responsibilities in the royal court. He is a work in progress, and the reasons behind his outlandish behavior are much debated by critics.
Hotspur, whose real name is Henry Percy, on the other hand, is an inarguably honorable character who stands in stark contrast to the more lackadaisical Hal. The son of the Earl of Northumberland, Hotspur is valiant in battle and actively seeks recognition for his military prowess. He is charismatic, brave, and loyal, exhibiting a sense of purpose and seriousness that Hal appears to be sorely lacking.
It is a tribute to Hal's perceptiveness that he recognizes the strength of character possessed by his rival. He says of Hotspur,
"I do not think a braver gentleman,
More active-violent or more valiant-young,
More daring or more bold, is now alive
To grace this latter age with noble deeds" (V.i.89-93).
Hal also astutely recognizes Hotspur's tragic flaw - although Hotspur is complex and unfailingly noble, he, unlike Hal, does not have the ability to live in the real world of his times, a world which Hal describes as "the vilest earth" (V.iv.91).
I would add that perception is a huge theme in this play, and must be taken into account when comparing these two characters. We see how the king perceives Hotspur (as noble and valiant and worthy to be a prince) and his own son Hal (as dissolute and uncaring). At the same time, the audience is given a peek at Hal's intent from the beginning, when Hal soliloquizes that he has an unannounced plan to throw off the inappropriate behaviors and appearances when the time is right:
Yet herein will I imitate the sun,
Who doth permit the base contagious clouds
To smother up his beauty from the world,
That, when he please again to be himself,
Being wanted, he may be more wonder'd at,
By breaking through the foul and ugly mists
Of vapours that did seem to strangle him. (I.2)
At the same time, Hotspur is a valiant, honorable man--with a nasty temper and sometimes, the cunning and tact of a three-year-old. He has focused all his energies on being a great warrior but he throws temper tantrums. He also sees no more than appearance in his enemy, Prince Hal, causing him to grossly underestimate the heir apparent on the battlefield, costing him his life. Hal may compliment Hotspur, as symatsuoka says, but that bespeaks his own graciousness and nobility more than Hotspur's worthiness of his praise.