It is well nigh impossible to recommend a definitive recording of Messiah because no definitive version of the work exists. Handel tinkered with it constantly, sprucing it up to fit the different specifications of the many performances he conducted. The autograph score of 1741 is different from the Dublin premiere copy of 1742. Handel presented different versions in London in 1743, 1745, 1749 and 1750. Then, of course, there's the Foundling Hospital incarnation of 1759. So we won't think "definitive" here, just good.
For a celebratory, large-scale Messiah that bucks the "period performance" trend, try Andrew Davis conducting the Toronto Symphony on EMI. The choruses ring out splendidly, with no apologies made for hefty doses of pomp and pageantry. Samuel Ramey can be a bit too plain for comfort in the bass solos, but the other singers are fine, especially the seraphic soprano, Kathleen Battle. The "Hallelujah," complete with prominent organ accompaniment, is as majestic as can be.
On a smaller scale is another Davis, Sir Colin, conducting a two-for-one Messiah release recorded by Philips over three decades ago. It does not ring out as profoundly as the other, but it is a vigorous, beautifully performed, quintessentially British account that will not disappoint. It stands up sonically as well, so don't let the budget price throw you. Has any bass ever delivered "the people that walked in darkness" with more proprietary flair than Howard County's own John Shirley-Quirk. No!
We don't usually associate Sir Georg Solti and the Chicago Symphony with the baroque era, but Solti's Messiah, employing a scaled-down complement of modern instruments, is very exciting and quite affecting for the soul. He didn't book the finest alto, mind you, but soprano Kiri Te Kanawa and her male colleagues are excellent.
English conductor John Eliot Gardiner's discography proves beyond a reasonable doubt that a dose of period performance consciousness needn't yield scratchy, scrawny results. So if you want to let yourself in for a bit of musical revisionism a la 18th-century performance practices, Gardiner could be your man. He uses female sopranos and altos, not hooty, straight-toned boys, and his "Hallelujah" is second to none.
One lovely novelty act comes from Sir Neville Marriner, who leads a re-creation of the 1743 London premiere of Messiah, full of musicological wrinkles you don't often hear. It's all wonderful, as re-released on London 444824. There are other Marriner Messiahs out there, but they don't come close.