Best months to trek in Nepal

  I have been getting some enquiries about which are the best months to trek in Nepal. More specifically, people want to know which is the  most busy month and how does spring trekking (March/April) compare to autumn (Oct/Nov)? Weather wise post monsoon Oct/Nov is the most stable and clear but Oct is also the most crowded. I generally like to avoid Oct as lodges are busy, trails are full and there are far too many people around.
Recently we have been trekking in December which is suitable for the foothills but not ideal for the high mountains e.g. Kala Pattar, Annapurna Base Camp etc.
So my recommendations would be for high altitude treks in  Nepal try April or mid to late November. For foothills trekking November-December would be fine. In fact Everest Kala Pattar trek would also be good in November before the winter snows set in.
Here are the statistics of trekkers in Everest and Annapurna for the last five years which gives a good idea of the numbers on the trail:

EVEREST REGION
	2005	2006	2007	2008	2009
Jan	426	486	566	642	576
Feb	524	455	592	853	658
Mar	2343	1977	3029	3688	3041
Apr	2458	3439	4246	4661	4513
May	937	886	1679	1986	1629
June	201	110	284	297	298
July	204	184	209	294	229
Aug	260	352	434	450	509
Sept	1016	1190	1458	2135	2535
Oct	6242	6595	7750	9260
Nov	3448	3323	4188	4830
Dec	984	1039	1379	1503
ANNAPURNA REGION
	2003	2004	2005	2006	2007
Jan	1842	2106	1877	2570	2555
Feb	2325	3096	1527	3029	3574
Mar	2955	5147	4621	6575	6473
Apr	5484	6021	3216	8261	7324
May	2228	1794	1051	3022	2377
June	782	789	390	1325	680
July	864	881	712	779	774
Aug	1489	1488	1445	2186	2112
Sept	4315	3353	3525	5306	5231
Oct	9576	9314	9547
Nov	5698	5116	5319
Dec	3110	2242	2954

The figures for Everest were collected from the entrance of the Sagarmatha National Park ( Jorsale) and the Annapurna data from the ACAP office at Birethanti.