any Hilton property will be fine. Arlington is literally just across the river from Downtown DC. The subway in the area (Metro) is your best bet for getting to/from downtown unless you really like to drive and is reached easily (short walk or quick but relatively not cheap taxi/uber) from any hotel.

DC area has some of the very worst commuting traffic in the country. In reality, AM rush hour is from 5:00 to 9:30am while PM rush is from 2:30 to around 8pm or later - so yes, depending upon what time you try to travel a 2 mile trip can take 30 minutes or more. The trip to my metro station takes 5 minutes door to door with no traffic but 30 minutes in the am and up to 45 in the pm.

Stay in Arlington - take metro.