Most pubs that would be busy in the afternoon are on Sauchiehall Street. Lauders is not far from Buchanan Galleries and always seems to be busy but the main clientele are older men, still a nice proper pub tho. Hengler's circus which is further up Sauchiehall Street towards Charing Cross is a Wetherspoons but is usually busy. The West End (Byres road and Ashon Lane) is usually busy as student types hang about here and drinking on an afternoon is not uncommon! It all depends on your age really. If its nice weather there are plenty of pubs you can sit outside on Ashton Lane and it is a nice area to sit in, but you will see a lot of students as its right beside Glasgow uni. Hope this helps