LineWhat actually matters (it isn't the bonus)
Every "best sportsbook" ranking on the internet is ordered by affiliate payout, which is why they all lead with sign-up bonuses. Bonuses are one-time, hedged with rollover terms, and identical in spirit everywhere. The attributes that compound over a betting lifetime are different: odds quality (a book that hangs -108 instead of -110 saves you real money on every bet forever), market depth (does it price the sports and props you actually bet), payout speed (days vs. hours matters when it's your money), and — the one nobody writes about — tolerance for winners. Most recreational-facing books limit accounts that show skill, sometimes to bet sizes measured in pocket change. If you intend to bet well, the book's limiting behavior matters more than every other feature combined.
The honest profiles
FanDuel and DraftKings are the two giants, and for most bettors the differences are cosmetic: both offer the deepest same-game-parlay engines, the widest prop menus, slick apps, and constant promos. Both are quick to limit winning players, and both carry higher hold on their promoted products than their main lines — the app is designed to walk you from the -110 spread to the 30%-hold SGP. Fine primary books for recreational, prop-heavy bettors; frustrating homes for sharps.
BetMGM and Caesars compete on the same recreational turf with comparable menus. Their differentiator is the casino-rewards ecosystems — meaningful if you'd use the hotel and comp side, irrelevant if you wouldn't. Odds quality is ordinary; limiting behavior is industry-standard.
ESPN Bet and Fanatics are the newer entrants buying market share, which historically means aggressive promos and occasionally soft, slow-moving lines — a genuine (if temporary) opportunity for line shoppers, since slow books are where stale numbers and middles live.
bet365 brings a global book's depth — obscure leagues, deep soccer markets — with a strong live-betting product. Internationally it's known for fast, aggressive limiting of winners; expect the same instinct domestically.
Exchanges and low-vig books (where legal in your state — availability varies widely) are the sharp-bettor answer: peer-to-peer or reduced-juice pricing means better numbers and, on true exchanges, no limiting for winning, because you're betting against other users rather than the house. Thinner markets and less polish are the trade.
The actual strategy: be a customer of several
The real answer to "which book is best" is plural. Line shopping — checking your bet's price at three or four books and taking the best number — is worth roughly a full point of win rate, which is more than most handicapping insights are worth, and it requires no skill beyond opening a second app. Two or three mainstream books plus one sharp/low-vig option covers most needs: the mainstream books for menu depth and promos while they last, the sharp option as your pricing benchmark and long-term home. Keep deposits modest everywhere, withdraw regularly (payout friction is a feature, not a bug, at some shops), and remember that every book's posted price is an opinion you're allowed to shop against.