We are staying in dubai for 5 nights and then 2 nights in abu dhabi whats the best transport method to get to abu dhabi ( staying in ethihad jumeriah towers ).
You can get a metered taxi...cream coloured one.
Agree with Clint - 'best' = reliable, not getting ripped off, being insured etc.
You may wish to 'upgrade' to a better car - the so-called limo (usually a Lexus saloon), but you'll pay at least 30% above the metered fare.
You may wish to use a guy someone knows, which may be cheaper, but potentially riskier if he's eitther a licensed driver 'doing it off the books' or using a private car when he's not registered nor insured to drive for reward.
Careem and Uber are also options if you'd like a choice of cars, but you'll be paying more than a taxi would cost.
You can opt for an intercity bus, runs from 5:30 am till midnight all days, at every 15-20 minute intervals. Costs AED 20/25 (not sure of current fare) per person, through NOL (Travel) card available at the ticket window in Dubai.
About 20% more than a standard cream coloured taxi so not sure why you'd bother with Uber unless, for some reason, you couldn't find a 7 seater standard taxi