The answer depends on your definition of the "best sex ratio". According to the U.S. Census Bureau, in 2010 Alaska had the highest ratio of men to women. The District of Columbia / Washington had the highest ratio of females to males.

		Male		Female		Male:Female ratio	Population age structure
State / Region	Total population	Number	Percent	Number	Percent	Males per 100 females	Median age	% under 18 years	% 18 to 44 years	% 45 to 64 years	% 65 and over
Alaska	710,231	369,628	52.0%	340,603	48.0%	108.52	33.8	26.4	38.2	27.7	7.7
Wyoming	563,626	287,437	51.0%	276,189	49.0%	104.07	36.8	24	35.7	27.9	12.4
North Dakota	672,591	339,864	50.5%	332,727	49.5%	102.15	37	22.3	36.7	26.5	14.5
Nevada	2,700,551	1,363,616	50.5%	1,336,935	49.5%	102.00	36.3	24.6	37.7	25.6	12
Utah	2,763,885	1,388,317	50.2%	1,375,568	49.8%	100.93	29.2	31.5	39.7	19.8	9
Montana	989,415	496,667	50.2%	492,748	49.8%	100.80	39.8	22.6	33.4	29.2	14.8
Colorado	5,029,196	2,520,662	50.1%	2,508,534	49.9%	100.48	36.1	24.4	38.1	26.7	10.9
Idaho	1,567,582	785,324	50.1%	782,258	49.9%	100.39	34.6	27.4	35.4	24.8	12.4
Hawaii	1,360,301	681,243	50.1%	679,058	49.9%	100.32	38.6	22.3	36.2	27.2	14.3
South Dakota	814,180	407,381	50.0%	406,799	50.0%	100.14	36.9	24.9	34.4	26.4	14.3
WEST	71,945,553	35,849,677	49.8%	36,095,876	50.2%	99.32	35.6	24.9	37.8	25.4	11.9
Washington	6,724,540	3,349,707	49.8%	3,374,833	50.2%	99.26	37.3	23.5	37.1	27.1	12.3
California	37,253,956	18,517,830	49.7%	18,736,126	50.3%	98.83	35.2	25	38.7	24.9	11.4
Arizona	6,392,017	3,175,823	49.7%	3,216,194	50.3%	98.74	35.9	25.5	36.2	24.5	13.8
Wisconsin	5,686,986	2,822,400	49.6%	2,864,586	50.4%	98.53	38.5	23.6	35.1	27.7	13.7
Minnesota	5,303,925	2,632,132	49.6%	2,671,793	50.4%	98.52	37.4	24.2	35.8	27.1	12.9
Nebraska	1,826,341	906,296	49.6%	920,045	50.4%	98.51	36.2	25.1	35.5	25.8	13.5
Kansas	2,853,118	1,415,408	49.6%	1,437,710	50.4%	98.45	36	25.5	35.5	25.8	13.2
Texas	25,145,561	12,472,280	49.6%	12,673,281	50.4%	98.41	33.6	27.3	38.4	24	10.3
Iowa	3,046,355	1,508,319	49.5%	1,538,036	50.5%	98.07	38.1	23.9	34.6	26.7	14.9
Oklahoma	3,751,351	1,856,977	49.5%	1,894,374	50.5%	98.03	36.2	24.8	36	25.8	13.5
Oregon	3,831,074	1,896,002	49.5%	1,935,072	50.5%	97.98	38.4	22.6	36.1	27.4	13.9
New Mexico	2,059,179	1,017,421	49.4%	1,041,758	50.6%	97.66	36.7	25.2	34.9	26.7	13.2
New Hampshire	1,316,470	649,394	49.3%	667,076	50.7%	97.35	41.1	21.8	33.9	30.7	13.5
West Virginia	1,852,994	913,586	49.3%	939,408	50.7%	97.25	41.3	20.9	33.8	29.2	16
Vermont	625,741	308,206	49.3%	317,535	50.7%	97.06	41.5	20.7	34	30.8	14.6
Kentucky	4,339,367	2,134,952	49.2%	2,204,415	50.8%	96.85	38.1	23.6	35.9	27.2	13.3
MIDWEST	66,927,001	32,927,560	49.2%	33,999,441	50.8%	96.85	37.7	24.1	35.4	27	13.5
Indiana	6,483,802	3,189,737	49.2%	3,294,065	50.8%	96.83	37	24.8	35.8	26.5	13
UNITED STATES	308,745,538	151,781,326	49.2%	156,964,212	50.8%	96.70	37.2	24	36.5	26.4	13
Arkansas	2,915,918	1,431,637	49.1%	1,484,281	50.9%	96.45	37.4	24.4	35.2	26	14.4
Virginia	8,001,024	3,925,983	49.1%	4,075,041	50.9%	96.34	37.5	23.2	37.5	27.1	12.2
Michigan	9,883,640	4,848,114	49.1%	5,035,526	50.9%	96.28	38.9	23.7	34.6	27.9	13.8
Illinois	12,830,632	6,292,276	49.0%	6,538,356	51.0%	96.24	36.6	24.4	37	26.1	12.5
SOUTH	114,555,744	56,134,681	49.0%	58,421,063	51.0%	96.09	37	24.3	36.7	26.1	13
Missouri	5,988,927	2,933,477	49.0%	3,055,450	51.0%	96.01	37.9	23.8	35.3	26.9	14
Louisiana	4,533,372	2,219,292	49.0%	2,314,080	51.0%	95.90	35.8	24.7	36.8	26.2	12.3
Maine	1,328,361	650,056	48.9%	678,305	51.1%	95.84	42.7	20.7	32.5	30.9	15.9
Florida	18,801,310	9,189,355	48.9%	9,611,955	51.1%	95.60	40.7	21.3	34.4	27	17.3
Ohio	11,536,504	5,632,156	48.8%	5,904,348	51.2%	95.39	38.8	23.7	34.6	27.7	14.1
Georgia	9,687,653	4,729,171	48.8%	4,958,482	51.2%	95.38	35.3	25.7	38.2	25.4	10.7
Tennessee	6,346,105	3,093,504	48.7%	3,252,601	51.3%	95.11	38	23.6	36	27	13.4
Pennsylvania	12,702,379	6,190,363	48.7%	6,512,016	51.3%	95.06	40.1	22	34.5	28	15.4
North Carolina	9,535,483	4,645,492	48.7%	4,889,991	51.3%	95.00	37.4	23.9	36.8	26.3	12.9
New Jersey	8,791,894	4,279,600	48.7%	4,512,294	51.3%	94.84	39	23.5	35.4	27.6	13.5
Connecticut	3,574,097	1,739,614	48.7%	1,834,483	51.3%	94.83	40	22.9	34.5	28.5	14.2
South Carolina	4,625,364	2,250,101	48.6%	2,375,263	51.4%	94.73	37.9	23.4	36.1	26.9	13.7
NORTHEAST	55,317,240	26,869,408	48.6%	28,447,832	51.4%	94.45	39.2	22.3	35.9	27.7	14.1
Mississippi	2,967,297	1,441,240	48.6%	1,526,057	51.4%	94.44	36	25.5	36	25.8	12.8
Alabama	4,779,736	2,320,188	48.5%	2,459,548	51.5%	94.33	37.9	23.7	35.7	26.8	13.8
Delaware	897,934	434,939	48.4%	462,995	51.6%	93.94	38.8	22.9	35.5	27.2	14.4
New York	19,378,102	9,377,147	48.4%	10,000,955	51.6%	93.76	38	22.3	37.4	26.7	13.5
Massachusetts	6,547,629	3,166,628	48.4%	3,381,001	51.6%	93.66	39.1	21.7	36.8	27.7	13.8
Maryland	5,773,552	2,791,762	48.4%	2,981,790	51.6%	93.63	38	23.4	36.6	27.7	12.3
Rhode Island	1,052,567	508,400	48.3%	544,167	51.7%	93.43	39.4	21.3	36.5	27.8	14.4
Puerto Rico	3,725,789	1,785,171	47.9%	1,940,618	52.1%	91.99	36.9	24.2	36.3	24.9	14.5
District of Columbia	601,723	284,222	47.2%	317,501	52.8%	89.52	33.8	16.8	48.6	23.2	11.4